Objectives. To report the initial results of treatment of outlet obstruction induced by benign prostatic hyperplasia (BPH) using interstitial laser coagulation performed with the Indigo 830 nm diode laser system. Methods. A group of 112 men with lower urinary tract symptoms caused by BPH underwent treatment with the indigo 830 nm laser system between October 1994 and November 1995. Patients were assessed prior to treatment and at specified post-treatment intervals for symptom score, uroflow, postvoid residual, and prostate volume. Adverse events and changes in laboratory parameters were monitored at each post-treatment visit to investigate safety of the procedure. Results. Symptom score decreased from 20.9 at initial measurement to 9.6 at 3 months after procedure and 7.9 at 6 months. Uroflow rate increased from 8.0 mL/s initially to 15.2 and 14.2 mL/s at 3 and 6 months, respectively. Residual bladder volumes decreased from 105 mL initially to 59 and 38 mL at 3 and 6 months, respectively. There were no major complications (impotence, sustained incontinence, significant blood loss). Minor complications occurred in a small number of patients but were generally associated with urinary tract infection in patients with catheters. Three patients (2.7%) required retreatment and underwent transurethral resection of the prostate. Conclusions. Interstitial laser coagulation using an 830-nm diode laser system appears to be a promising new treatment, with substantial improvements in objective and subjective parameters of obstruction and a favorable side-effect profile.