Aim: To evaluate the influence of clear cornea phacoemulsification on filtering bleb morphology, function, and intraocular pressure (IOP) in glaucomatous eyes with previously successful filtering surgery. Methods: The clinical course of 30 patients (30 eyes) who underwent clear cornea phacoemulsification after successful filtering glaucoma surgery was prospectively evaluated. Mean IOP and filtering bleb morphology (standardised assessment criteria and score 0–12, 12= optimum) were determined before surgery, and 3 days, 6 months, and 12 months after surgery. The control group consisted of 36 patients with glaucoma after clear cornea phacoemulsification without previous filtering surgery. Results: Mean IOP increased after phacoemulsification by about 2 mmHg (preoperatively 14.28 (SD 3.71) mmHg, 12 months postoperatively 16.33 (3.31) mmHg, p = 0.006). 15 patients (50%) showed an IOP increase of .2 mmHg, 11 patients (36.7%) had no IOP difference (within 2 mmHg), and in four patients (13.3%) IOP decreased .2 mmHg. Mean score of filtering bleb morphology 1 year after surgery decreased from 9.5 to 9.0 (p = 0.154). In three of 30 preoperatively IOP regulated eyes the postoperative IOP was 21 mmHg. The control group showed an average IOP decrease of 2.01 mmHg (p = 0.014) 12 months after cataract surgery. Conclusion: An increase in IOP was found 1 year after phacoemulsification in half of the filtered glaucomatous eyes. IOP in glaucomatous eyes without previous filtering surgery decreased in the same period. Cataract extraction using clear cornea phacoemulsification may be associated with a partial loss of the previously functioning filter and with an impairment of filtering bleb morphology.