This study compares the outcomes of transscleral diode laser cyclo-photo-coagulation with the treatment parameters used. This was a retrospective chart review of a random sample of diode laser procedures using the G-probe over 10 years for uncontrolled glaucoma. The main outcome measure was intraocular pressure (IOP) reduction by 20% and final IOP ≤21mmHg. In 236 eyes (patients) treated by five glaucoma specialists, most eyes had severe refractory glaucoma, with 75% having <20/200 visual acuity. Median follow-up was 2.7 years. In eyes receiving only one treatment, IOP success criterion was met in 72% (129/180). Success was significantly related to power per delivery and median total joules per treatment (successes=135 J, failures=98 J; P=0.0009), but not to number of deliveries, nor to extent of circumference treated. Greater success was associated with three or four second duration per delivery, power level based on audible cues, and firm pressure on the sclera. Using a standard 2000mW, two seconds, 20 deliveries in each eye had the lowest success rate (49%). Of those with no preoperative pain, 40 patients (57%) had no postoperative pain, whereas 20 reported pain of 1-3/10 (29%). Phthisis occurred in seven eyes (3%), five of which had severe secondary eye disease. Nine eyes had no light perception (NPL) preoperatively, whereas 50 eyes were NPL at last follow-up, many after additional surgeries for other conditions. Diode cyclophotocoagulation achieved reasonable IOP lowering, often without postoperative pain or complications. Greater success was achieved when audible effects were used to tailor the power settings to individual responses. Diode treatments with no intraoperative effect adjustment or using standardised protocols may not achieve optimal success.