AIM: Suture lysis is commonly performed after trabeculectomy to improve bleb function. It is often thought to be an innocuous procedure. This is the first large study to determine the safety of the procedure and compare results with a control group. METHODS: Two hundred successive trabeculectomies performed between January 1992 and October 1993 were analysed. RESULTS: Ninety nine eyes underwent trabeculectomy and suture lysis; 101 eyes underwent trabeculectomy and did not require postoperative suture lysis. The following complications were noted with suture lysis: flat chambers (13.1%), external aqueous leaks (9%), malignant glaucoma (2%), iris incarceration (2%), and large blebs (2%). All resolved with appropriate management. There was no significant difference in the final postoperative mean pressures between the lysis and the non-lysis groups. CONCLUSION: Suture lysis is not an innocuous procedure. However if managed appropriately, complications do not affect the intraocular pressure outcome.