Surgical treatment in a West Indian black population with primary open angle glaucoma was randomized to full-thickness posterior lip sclerectomies or partial-thickness trabeculectomies. Forty-five posterior lip sclerectomies and 35 trabeculectomies were performed. With a mean follow-up period of 28.3 months, the eyes with posterior lip sclerectomies had lower intraocular pressures, reduced glaucoma medication requirements, and less failures. Decline of visual acuity did not differ significantly between the two groups, but early visual acuity loss due to accelerated cataract formation was noted more frequently with posterior lip sclerectomies. The incidence of flat anterior chambers also did not differ significantly, but shallow anterior chambers were more frequent and persisted for a longer time with posterior lip sclerectomies. Other complications were more frequent with posterior lip sclerectomies.