• Posterior scleral trephination at the pars plana ciliaris in a dependent site, with normal conjunctiva covering the opening, proved a reliable method for evacuating subchoroidal effusion in cases of flat anterior chamber. The method was also successful in cases occurring after retinal detachment surgery and after expulsive hemorrhage. Unlike linear sclerotomy, drainage of the subchoroidal effusion continues for several days after the trephination.