- The solo instrument that produces the melody in the title music is a theremin. It was invented by Russian scientist Leon Theremin and was first demonstrated in 1920. It predates the modern synthesizer by about 40 years, but its uniqueness stems from the fact that it is the only instrument that is played without actually being touched. Its electronic circuits are controlled by two antennas, left and right of the instrument, toward which the player moves his or her hands. The closer the right hand to one antenna, the higher the pitch. Similarly the proximity of the left hand to the other antenna controls the volume. The theremin has a range well in excess of eight octaves, and is capable of all kinds of strange effects. These sounds have been put to use in science fiction and other films including Alfred Hitchcock's Spellbound and Robert Wise's The Day the Earth Stood Still. This unique instrument has also been used on The Beach Boys' song "Good Vibrations." The late Clara Rockmore was the theremin's greatest virtuoso, and the instrument and its inventor were profiled in the documentary Theremin: An Electronic Odyssey (1994).
- Ian Richardson was booked for a role but died before filming.
- Filming for an episode "The Blood Point" was abandoned after a few preliminary pickup-up shots had been filmed because of unintentional close similarities between the plot and a real-life event.
- SPOILER: As of 2011 there have been 200 murders in Midsomer, including 12 from poisoning (one from a tropical frog), 9 drownings (one in a vat of soup), 6 burned to death (one in a straw effigy) and even 4 villagers killed by bow and arrow.
- In an article in the 19 March 2011 edition of the Radio Times listings magazine, producer Brian True-May was quoted as saying about Midsomer Murders: "We don't have ethnic minorities involved. Because it wouldn't be the English village with them. It just wouldn't work. Suddenly we might be in Slough. Ironically, Causton is supposed to be Slough. And if you went into Slough you wouldn't see a white face there. We're the last bastion of Englishness and I want to keep it that way. I'm trying to make something that appeals to a certain audience, which seems to succeed. And I don't want to change it." He was suspended for these comments, perceived to be racist, which provoked a lot of discussion in the media, with opinions polarized in favor or in opposition with the policy. He was later reinstated but it was announced that he would step down as producer after the 2011 series had finished.
- A large number of actors have appeared in more than one episode of Midsomer Murders, sometimes as characters in an episode after their first incarnation has been horribly murdered. The first time this happened was with Richard Cant and Elizabeth Spriggs, who appeared in the episode Dead Letters (2006) nine years after they had both been murdered in the episode The Killings at Badger's Drift (1997). They played close relatives of their previous characters and D.I. Barnaby commented on the uncanny resemblance. Other actors who have "come back from the dead" in this way include Felicity Dean and Anna Massey.
- First entry in the popular series.
- The mother and son characters of Iris and Dennis Rainbird are related (as sister and cousin respectively) to Ursula and Alistair Gooding (again mother and son), characters in "Midsomer Murders" (1997) {Dead Letters (#9.2)}. Both sets of characters were played by Elizabeth Spriggs and Richard Cant.
- SPOILER: When filming his death scene, Richard Briers did all his stunts, refusing to let a stuntman do it.
- Hector Bridges wears the regimental tie of the Royal Irish Fusiliers. It would be a question as to whether he served in that unit, because it was amalgamated in 1968 (with the Royal Inniskilling Fusiliers and the Royal Ulster Rifles) and thenceforth was known as the Royal Irish Rangers.
- Last TV role of 'Phylis Calvert'.
- SPOILER: This is the only episode of Midsomer Murders (UK) in which no murders are committed. The episode deals with euthanasia.
- When the gardening expert is shown filming his TV show, the crew in the background are actually the real Midsomer Murders production crew, including the director hunching over his monitor.
- During the scene in the tent at the festivities, the community youth orchestra is doing their best to actually play the Midsomer Murders theme.
- Last TV role of Edward Jewesbury.
- The elderly Peter, Marquis of Ross, is played by Laurence Penry-Jones. His son Peter Penry-Jones plays the marquis as a young man, forty years earlier in flashback.
- When the police are looking through a victim's room, there is a framed poster of Louise Brooks on the wall.
- Reggie's comment about pilots shooting at the Luftwaffe with their service revolvers is actually based in fact. During a daylight raid against Bergen in January 1945, Flight Lieutenant Ray Harris, flying Lancaster Willing Willie with 9 Squadron, drew his service revolver and fired at White 11, the FW-190A-8 of Unteroffizier Heinz Orlowski, who had flown alongside the Lancaster to salute the pilot, in the belief that the damage that had been inflicted would prevent the aircraft from returning home. (Chapter 1 of 'Lancaster: The Biography' by Sqd Ldr Tony Iveson, DFC and Brian Milton. ISBN 978-0-233-00270-5)
- A rarity in the series, if not the only one, there is no pathologist called in on any murder. However, there is a visiting pathologist, Clare Holman, the pathologist for Inspector Morse and Inspector Lewis, appears as one of the cast members.
- James Hazeldine died a few weeks before broadcast.
- The author of the book that is the root of the strife between the two villages is Ellis Bell. Ellis Bell was the pseudonym of Emily Brontë.
- The character of Alan Clifford's nurse, Agnes Waterhouse, is named after the first witch to be executed in England (hanged, not burned, in 1566).
- Clare Bonavita calls her protégé Henry Charlton "Midsomer's answer to Steve Redgrave". Redgrave plays the talent scout from the Olympic Committee who is at the regatta to have a look at Charlton.
- Captain Tucker wears the regimental tie of the Brigade of Guards; Munro Hilliard wears the club tie of the Marylebone Cricket Club.
- One of the few episodes whose end-credits music is not the usual Midsomer Murders theme - this one is a continuation of the "Midsomer Rhapsody" piece featured throughout the episode.
- Last appearance of John Hopkins as DS Dan Scott.
- The estate agent selling Arthur Leggott's house is shown on the sign as "Beauvoisin", a possible reference to the character of Olive Beauvoisin who appeared in the Midsomer episodes "Death's Shadow" and "Dead Man's Eleven."
- The first series entry to feature Jason Hughes as Constable Ben Jones.
- The mother and son characters of Ursula and Alistair Gooding are related (as sister and cousin respectively) to Iris and Dennis Rainbird (again mother and son), characters in the very first episode, "Midsomer Murders" (1997) {The Killings at Badger's Drift (#1.1)}. Both sets of characters were played by Elizabeth Spriggs and Richard Cant.
- In the last seconds of Dead Letters we see, on a book rack in the small lending library, a copy of Chromosome Wars by Jezebel Tripp, the author we met in Sins of Commission from season 7.

