Sector 21527 was a sector of space near the Cardassian system. An asteroid field was located in this sector.

In 2369, Lieutenant Commander Geordi La Forge used Stellar Cartography to find an astronomical object in this sector and found the McAllister C-5 Nebula. (TNG: "Chain of Command, Part II")

In 2370, the USS Enterprise-D performed tests of new weapons systems in this sector. Later, when the ship's crew was disabled by Barclay's Protomorphosis Syndrome, the Enterprise-D became adrift in this sector. (TNG: "Genesis")