OBJECTIVE: To analyze the results of trabeculectomy performed for all cases of acute primary angle closure (APAC). DESIGN: Retrospective, noncomparative case series PARTICIPANTS: Fifty-six consecutive patients who underwent trabeculectomy for APAC at two Singapore centers from 1993 through 1995. METHODS: The conventional treatment for APAC is to lower intraocular pressure (IOP) medically, after which laser peripheral iridotomy (PI) is performed. However, in Asian eyes, the acute attack is often refractory to standard treatment. Trabeculectomy is occasionally performed on eyes that do not respond to medical therapy, as well as eyes with APAC that respond to medical therapy but are assessed as having underlying chronic angle-closure glaucoma. In such cases, laser PI is not performed before trabeculectomy. MAIN OUTCOME MEASURES: The surgical outcome was assessed in terms of final IOP and the incidence of complications. Success was defined as final IOP less than 21 mmHg without medication, and qualified success was defined as final IOP less than 21 mmHg with medication. Patients whose IOP was more than 21 mmHg, required further glaucoma surgery, lost light perception, or whose eye became phthisical were classified as failures. RESULTS: The mean follow up was 22 months (range, 6-42 months). In group A, the medical failure group (n = 32), success in IOP control was obtained in 18 patients (56.2%), qualified success was achieved in 3 patients (9.4%), and failure resulted in 11 patients (34.4%). Ten patients (31.3%) encountered early postoperative complications such as shallow anterior chamber. In group B, the medical success group (n = 24), success in IOP control was achieved in 21 patients (87.5%), qualified success was achieved in 3 patients (12.5%), and there were no cases of failure. The incidence of postoperative complications was low (4 eyes [16.7%]). In terms of IOP outcome, trabeculectomy outcome was significantly worse in group A (P<0.001, Fisher's exact test). CONCLUSIONS: Because there is a high risk of surgical failure and complications, trabeculectomy may not be the procedure of choice in medically unresponsive cases of APAC.