When the doctor drains a sebaceous cyst does it always have to be removed later.

Probably better. Your cyst was simply drained this time because it became infected and probably abscessed. This leaves a good portion of the capsule behind and the cyst will reform. It may become infected again so usually better to have removed completely once this infection resolves.
Excision needed. Yes, the sebaceous cyst will recur if any part of the wall of the cyst is left behind. Your doctor will allow the infection to settle and then schedule you for excision of the cyst.

Related Questions

Do I need to go to the doctor to drain an unsightly, painful sebaceous cyst on my neck? It won't pop and I see white pus inside.

Cyst. Always a good plan to seek medical evaluation and possible I&D of infected cyst of neck. Also PO antibiotics are a must. If truly infected than only drainage is possible. Than after healing re excision of the scar and lining of the cyst is needed to prevent recurrence... Read more...