- For information dealing with this year in the timeline of the fictional Star Trek universe, see 1990.
1990
January
- Week of 1 January
- TNG: "The Defector" airs.
- Week of 8 January
- TNG: "The Hunted" airs.
- Week of 29 January
- TNG: "The High Ground" airs.
February
- Week of 5 February
- TNG: "Deja Q" airs.
- Week of 12 February
- TNG: "A Matter of Perspective" airs.
- Week of 19 February
- TNG: "Yesterday's Enterprise" airs. Denise Crosby makes her first guest appearance on TNG since her departure in 1988
March
- Week of 12 March
- TNG: "The Offspring" airs.
- Week of 19 March
- TNG: "Sins of the Father" airs.
- Week of 26 March
- TNG: "Allegiance" airs.
April
- Week of 2 April
- TNG: "Captain's Holiday" airs.
- Week of 23 April
- TNG: "Tin Man" airs.
- Week of 30 April
- TNG: "Hollow Pursuits" airs, the first to feature Dwight Schultz as TNG and later VOY recurring character Reginald Barclay.
May
- Week of 7 May
- TNG: "The Most Toys" airs.
- Week of 14 May
- TNG: "Sarek" airs. Mark Lenard guests as Ambassador Sarek, the first major crossover appearance of an original series character.
- Week of 28 May
- TNG: "Menage a Troi" airs.
June
- Week of 4 June
- TNG: "Transfigurations" airs.
- Week of 18 June
- TNG: "The Best of Both Worlds" airs and is the first cliffhanger of the series. Jean-Luc Picard is assimilated by the Borg and becomes Locutus of Borg, fueling rumors that Patrick Stewart may be leaving the series.
Summer
- Summer
- Production begins on TNG Season 4.
September
- Week of 24 September
- Star Trek: The Next Generation enters its fourth season, resolving the Borg story with "The Best of Both Worlds, Part II." Picard is rescued and Stewart remains a member of the TNG cast.
- 26 September
- Star Trek: The Next Generation premieres in the UK on the BBC.
October
- Week of 1 October
- TNG: "Family" airs.
- Week of 8 October
- TNG: "Brothers" airs.
- Week of 15 October
- TNG: "Suddenly Human" airs.
- Week of 22 October
- TNG: "Remember Me" airs.
- Week of 29 October
- TNG: "Legacy" airs.
November
- Week of 5 November
- TNG: "Reunion" airs.
- Week of 12 November
- TNG: "Future Imperfect" airs.
- Week of 19 November
- Wil Wheaton's final episode as a regular TNG castmember, "Final Mission," airs.
December
Other events
- 5 January
- Bart LaRue dies.
- 10 May
- Susan Oliver dies.
- 18 May
- Jill Ireland dies.
- 25 May
- Vic Tayback dies.
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