The occurrence of ptosis after trabeculectomy has been a common postoperative complication. Many factors have been implicated in the development of postoperative ptosis. The purpose of this study was to investigate the incidence of ptosis following trabeculectomy and whether or not it was influenced by combined cataract surgery, type of conjunctival flap, and previous intraocular surgery. We reviewed 386 eyes of 386 patients who underwent either trabeculectomy alone or trabeculectomy combined with cataract surgery, with greater than 6 month follow-up. Ptosis occurred in 10.7% (18 of 150 eyes) after trabeculectomy alone and in 12.7% (30 of 236 eyes) after trabeculectomy with combined cataract surgery (p = 0.96). The incidence of ptosis was 12.3% (10 of 81 eyes) after limbus-based conjunctival flap and 12.5% (38 of 305 eyes) after fornix-based conjunctival flap (p = 0.98). There was no significant difference in the incidence of ptosis between primary surgery eyes (12.5%, 34 of 273 eyes) and secondary surgery eyes (12.4%, 14 of 113 eyes) (p = 0.97). The incidence of ptosis after trabeculectomy was about 12% overall and not significantly influenced by combined cataract surgery, type of conjunctival flap or previous ocular surgery.