Purpose: To measure cataract changes quantitatively in the crystalline lens after trabeculectomy with mitomyfin C and to identify associated clinical factors. Methods: Forty-one consecutive trabeculectomy patients (41 eyes) were enrolled in this prospective study. The enrollment criteria were: phakic eye, no history of intraocular surgeries or inflammation, and no corneal opacification. The transparency of the lens uas, measured and analyzed by an anterior segment analysis system preoperatively and 1, 3, and 12 months postoperatively. Cataract development was correlated with clinical factors using a multivariate regression analysis. Results: During the first postoperative month, changes occurred primarily in the anterior segment of the lens, but later, deeper lenticular areas also started to show an increase in light scattering intensity. Multivariate regression analyses demonstrated that some clinical factors were associated with cataract development. Conclusions: Slight cataractous changes develop after trabeculectomy with mitomycin C as early as 1 month postoperatively, and they gradually increase in extent and intensity during the next 11 months. (C) 2000 Japanese Ophthalmological Society.