A series which, by design, does not run regularly. It may be a series of annual made-for-TV movies, or a series composed of Mini Series airing every few years (But lacking the regularity of a Television Serial). Often happens when a Pilot Movie sparks enough interest to prompt a second movie, but not enough to prompt a regular series.
In the US, these are typically revivals of series which were originally regular in format. They are far more common in the UK. British Irregular Series are often aired on public television in the US as part of a Genre Anthology such as Mystery or Masterpiece Theatre.
See also Inconsistent Episode Lengths for when the length of each episode is what's irregular, rather than the publication schedule.
- Lupin III has made six regular anime series, but has run for over twenty years as an annual series of made for TV movies in Japan. Link to the list: Lupin III Yearly Specials
- Rumiko Takahashi's Mermaid Saga, a manga variation of this, was periodically released in episodic stories over the course of ten years.
- When Tim Drake was introduced as the new Robin, he appeared in numerous mini-series before his ongoing started.
- For its first few years, IDW Publishing's Transformers series consisted of multiple mini-series and a 12-issue event series before receiving an ongoing.
- Adam Dalgliesh: The Roy Marsden adaptations consisted of TV movies and mini-series, with releases spanning from 1983 to 1998.
- Unlike regular panel shows, Big Fat Quiz of the Year is a yearly feature-length special that airs around Christmastime. Big Fat Quizzes with other topics (BFQ of Everything, decade-themed quizzes) vary from year to year with no set release schedule.
- Columbo started life as a Made-for-TV Movie, then became a series which aired as every third episode of The NBC Mystery Movie. Later, it became a series of TV Movies which aired with decreasing frequency.
- The Foyle's War series that were produced following the show's un-cancellation became more noticeably irregular in their release, with gaps of 2-3 years between series.
- Hetty Wainthropp Investigates: The pilot aired in 1990, whereas the four series aired 1996-98.
- The Incredible Hulk (1977): A four-year regular series sandwiched between two pilot movies and three made-for-TV-movies.
- Inspector Morse aired as a number of Mini Series.
- Jonathan Creek: Aired as a combination of specials and series, most notably with three specials released during 2009-2013, which came between the fourth (2003-2004) and fifth (2014) full series of the show.
- Marple: Each of the six series, aired between 2004 and 2013, contains 3-4 feature-length episodes.
- Perry Mason ran regularly from 1957-1966, then was revived for a series of TV movies in the 90s.
- Poirot ran from 1989 to 1993, then became a series of feature-length specials whose releases spanned almost two decades.
- The format switched to "series of TV movies" in 2009 to allow the actors to follow up on other commitments that a full-scale TV schedule would conflict with.
- Prime Suspect: Aired one series per year from 1991-96 (skipping 1994) then the final two series aired in 2003 and 2006, respectively.
- Psych became one following its original eight-season run, as installments thereafter are made-for-TV movies.
- The Rockford Files became a series of TV Film for a time after the regular series ended.
- Rumpole of the Bailey: Released intermittently from 1978 to 1992.
- Sharpe: Also ran like this, with a really noticeable time skip between the most recent installments.
- Sherlock consists of four three-episode series, with a two-year gap (or three, in the case of the fourth series) between them.
- The German language crime television series Tatort. 1971 saw 11 episodes, 2008 saw 31, and not evenly distributed to boot. In the first twenty years, the length of episodes varied, too, up to two hours; more recently things settled on about one and a half hours.
- The Thick of It: The first two series aired in 2005, followed by specials in 2007, a third series in 2009, then a fourth and final series in 2012.
- The British documentary series/social experiment Up takes this to extremes by airing a single instalment every seven years. It started by showing the participants at seven years old, and has gradually charted their lives in seven-year intervals ever since.