We aimed to evaluate the effect of nonpenetrating glaucoma filtration surgery on axial length (AL). Thirty patients (30 eyes) who underwent successful nonpenetrating glaucoma filtration surgery were prospectively analyzed. AL was measured preoperatively and postoperatively at 1 and 12 months. Associations between change in AL and age, gender, diagnosis, preoperative and postoperative visual acuity, refraction and intraocular pressure (IOP) were analyzed. AL decreased in 22 of 30 eyes postoperatively. The mean change in AL measurement was -0.15 +/- 0.27 mm (range -1.37 to +0.12 mm) at 1 month. Regression analysis showed that young age, a high preoperative IOP and a greater change in IOP were associated with a greater decrease in AL (p < 0.02). The mean AL at 12 months was almost the same as the preoperative value (p >0.2), but was significantly greater than the mean AL 1 month postoperatively (p = 0.001). There was no statistically significant difference between the IOP levels obtained postoperatively at 1 and 12 months (p >0.1). Nonpenetrating glaucoma surgery can result in a small decrease in AL which can reverse during the follow-up period. Copyright (C) 2003 S. Karger AG, Basel.