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 MiniSeries airing every few years (But lacking the regularity of a TelevisionSerial). Often happens when a PilotMovie sparks enough interest to prompt a second movie, but not enough to prompt a regular series.

In the US, these are typically [[{{Revival}} revivals]] of series which were originally regular in format. They are far more common in the UK. British IrregularSeries are often aired on public television in the US as part of a GenreAnthology such as ''Series/{{Mystery}}'' or ''Series/MasterpieceTheatre''.

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!!Examples

* ''Series/{{Columbo}}'' started life as a MadeForTVMovie, 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.
* ''TheRockfordFiles'' became a series of TV {{Film}} for a time after the regular series ended.
* ''Franchise/PerryMason'' did the same.
* As did ''Series/TheIncredibleHulk''.
* ''InspectorMorse'' aired as a number of MiniSeries.
* ''Series/HettyWainthroppInvestigates'' did as well.
* And ''SecondSight''
* And ''AdamDalglishMysteries''
* And ''PrimeSuspect''
* ''Series/{{Poirot}}'' in recent years.
** And in 2009, it will temporarily switch to the "series of TV movies" format to allow the actors to follow up on other commitments that a full-scale TV schedule would conflict with.
* ''Series/RumpoleOfTheBailey''.
* RumikoTakahashi's MermaidSaga, a manga variation of this, was periodically released in episodic stories over the course of ten years
* ''{{Sharpe}}'' has also ran like this, with a really noticeable time skip between the most recent instalments.
* 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.
* ''Series/TheThickOfIt''
* ''Anime/LupinIII'' has made four 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: Anime/LupinIIIYearlySpecials
* Non-television example: When Tim Drake was introduced as the new Robin, he appeared in an IrregularSeries before his regular series started.
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