In a retrospective study, 24 patients who had undergone simultaneous bilateral trabeculectomy over a 6-year period were reviewed. The duration of disease was at least 2 years, indicating that surgery was not performed as a primary procedure. No patients suffered complications leading to bilateral blindness, although 6 (25%) patients had reduced vision in both eyes at the first postoperative visit, with 3 (13%) worse than 6/36 binocularly. There was no evidence of an asymmetric response in the fall in intraocular pressure following trabeculectomy, after a mean follow-up of over 3 years. Compared with a matched group of patients undergoing unilateral trabeculectomy, the simultaneous bilateral group had a similar period of hospital stay. However, this was no shorter than that found in a group having staged bilateral surgery during the same admission, over the same study period. When separate admissions were required for bilateral drainage operations, though, there was a significant increase in the total length of inpatient stay. No convincing advantage was found for simultaneous bilateral trabeculectomy.