Is surgery required to remove large sebacious cyst from buttock?

Yes: So in general sebaceous cysts will not every completely go away unless they are removed. This requires a minor surgery. How minor depends on the size of the cyst. These can be often be done in the office under local anesthesia if done early when they are small, however, if large enough may require more than just local anesthesia. Best is to consult with a surgeon - general or plastic surgeon.