Previous studies have reported cataract surgery post trabeculectomy to be detrimental to IOP control. Conversely, other studies have reported phacoemulsification performed before trabeculectomy as a factor for bleb failure. The objective of this retrospective case control study was to evaluate the effect of phacoemulsification performed before or after trabeculectomy on IOP control. Forty-eight patients with primary open angle glaucoma (POAG) or primary angle closure glaucoma (PACG) were followed up for two years after trabeculectomy surgery. Eighteen patients had phacoemulsification subsequent to trabeculectomy (trab_phaco), and 30 patients were pseudophakic for greater than six months preceding trabeculectomy (phaco_trab). The primary outcome measures were target IOPs of A, ≤12mmHg; B, ≤15mmHg; C≤18mmHg with (qualified success) or without (unqualified success) additional topical treatment. Bleb failure was defined as the clinical need for additional topical antiglaucoma medication or further surgical intervention to achieve adequate IOP control. Bleb massage, suture removal or lysis, and postoperative 5-FU injections performed in clinics were permitted without constituting qualified success or failure. Results showed no significant difference in achieving the qualified and unqualified target IOPs in all groups A to C. In the first 12 months, significantly more trabeculectomies failed in the trab_phaco group (39%) compared with the phaco_trab group (10%). However, although this trend continued, failure rates between the two groups were not significant at 24 months.