AIMS: To study prospectively the success rate and complications of deep sclerectomy with collagen implant (DSCI), a new non-penetrating filtration procedure. METHODS: Non-randomised prospective trial involving consecutive patients. 100 eyes of 100 patients with medically uncontrolled primary and secondary open angle glaucoma. A superficial scleral flap was raised and a deep sclerectomy was performed in the scleral bed. Schlemm's canal was opened and dissection of the cornea was performed up to Descemet's membrane, at which point aqueous percolated through the remaining trabeculo-Descemet's membrane. A collagen implant was sutured radially in the scleral bed. Visual acuity, intraocular pressure (IOP) measurements, and slit lamp examinations were performed before surgery and after surgery at 1 and 7 days, and 1, 3, 6, 9, 12, 18, 24, 30, and 36 months. RESULTS: The mean follow up period was 17.8 (SD 8.7) months. The mean preoperative IOP was 27.8 (8.6) mm Hg; the mean postoperative IOP was 5.7 (4.0) at day 1, 11.2 (4.6) at month 1, 14.0 (3.5) at month 12, and 13.0 (3.8) at month 36. Complete success rate, defined as an IOP lower than 21 mm Hg without medication, was 44.6% at 36 months. Qualified success rate, defined as an IOP lower than 21 mm Hg with medication, was 97.7% at 36 months. Early postoperative complications included hyphaema in seven patients, would leak in 10 patients, and subtle choroidal detachment in 11 patients. Goniopuncture was performed in 41 of the patients, and 5-fluorouracil injections were made in 23 patients; cataract progression occurred in seven patients. When comparing the different types of open angle glaucoma, no difference was found in terms of reduction in IOP, number of patients requiring antiglaucoma medications, or success rate. CONCLUSIONS: Deep sclerectomy with collagen implant appears to provide reasonable control of IOP at medium term follow up, with few immediate postoperative complications.