Episode 5.1, "One Minute to Midnight", was originally filmed and aired as episode 4.22 in Europe.

Episode 5.19, "Double Jeopardy" was originally filmed and aired as Episode 4.19 in Europe.

Episode 5.2, "Prophecy," was originally aired filmed and aired as episode 5.1 in Europe.

Many of the episodes of the series have French actors with their voices redubbed by Vancouver-based voice actors Gary Chalk and Janyse Jaud.

The series directly follows the feature film Highlander (1986), but with a slight twist: according the series, Connor MacLeod was not the last Immortal and did not win the Prize. In fact, 'Christopher Lambert' guest stars in the pilot episode to pass the baton to series lead Adrian Paul.

Some of the clips used in the title sequence were taken from the movie Highlander II: The Quickening (1991).

Early in the second season, Alexandra Vandernoot told the producers she didn't want to be on the show anymore - which lead the writers to kill her off in "The Darkness".

The season five finale, "Archangel", was originally shot with a cliffhanger ending set 20 years in the future, when MacLeod is finally prepared to defeat Ahriman. The sixth season was planned to happen in the future, but was deemed too dark early on and was finally scrapped when the budget was sliced.

Jim Byrnes, who plays Joe Dawson, also contributed many songs to the show's soundtrack. Some of these can frequently be heard as background music during scenes in Joe's bar.

The character 'Duncan MacLeod' was ranked #11 in TV Guide's list of the "25 Greatest Sci-Fi Legends" (1 August 2004 issue).

Plans for a spin-off series led to a group of sixth-season episodes focusing on a new female Immortal (a "back-door pilot" in industry-speak). None of these characters caught on, and the established character of Amanda (Elizabeth Gracen) became the lead for "Highlander: The Raven" (1998).

A late fifth season episode, which partly depicted a fictional inspiration for Frankenstein, used the book's subtitle of "The Modern Prometheus".

Werner Stocker had already died of cancer before the end of the first season, so that episode (which opened with his character's murder) edited together existing footage from earlier episodes for the first scenes.

The series was originally planned to follow the film, with Connor Macleod in the lead role, to be played by Adrian Paul. Paul, however, wanted the freedom to create his own characterization, and to avoid direct comparisons to Christopher Lambert, so the writers agreed to create a new character.

Joe Dawson (the character ultimately played by Jim Byrnes) was originally going to be named Ian Dawson, and was conceived to be a bookish historian with less world experience than Joe. Actors considered for the role included Michael York and David McCallum.

The character of "Matthew McCormick," the immortal who works as a federal agent tracking serial killers, was created specifically for actor Eric McCormack. The producers even considered giving him his own Highlander spin-off series, in which McCormick would travel the country where ever there was a series of beheadings and "investigate" the crimes while simultaneously dispensing immortal justice.

Actor Alastair Duncan was considered for the lead role in the series. He later made a guest appearance as immortal Terence Coventry.