To determine the indications for postoperative radiotherapy after surgical resection of a nonfunctioning pituitary macroadenoma. A retrospective chart review of 72 patients with histologically proven chromophobe adenoma who presented for pituitary surgery between January 1985 and June 1998, with a minimum follow-up period of 12 months. The study endpoint was tumour recurrence or progression detected either by routine follow-up imaging or by clinical progression with subsequent confirmation by imaging. A proportional hazards model was used to determine independent prognostic factors. Mean follow-up was 64 months. In the radiotherapy group 13 of 50 recurred (or progressed) (26%), while in the nonradiotherapy group 10 of 22 recurred (46%), logrank test, P = 0.025. In patients assessed as having complete excision of tumour (n = 20) only two recurred (10%), both in patients without radiotherapy. No further treatment has been required in either case to date. In patients with residual tumour (n = 52), 41 had radiotherapy with 13 recurrences (32%), while 11 patients had no radiotherapy with eight subsequent recurrences (73%); logrank test, P = 0.007. Further treatment has been required in the majority of these cases. Cox's proportional hazards model analysis showed that only complete tumour removal and postoperative radiotherapy were independent favourable prognostic factors. The goal of surgery should be complete surgical excision where possible. The risk of recurrence in patients with no residual tumour on postoperative imaging is low enough to justify withholding routine postoperative radiotherapy in this group. In patients with residual tumour, conventional external beam radiotherapy administered within 12 months of surgery is effective at reducing recurrence or progression.