We report our experience with interstitial laser coagulation of the prostate (ILCP) using an Indigo 830j diode laser system for benign prostatic hyperplasia (BPH). From March 1998 to November 2000, we treated 45 patients between 51 and 95 years old (average 71.5) with symptomatic BPH. The mean prostatic volume before ILCP was 62.0 cm3. We experienced no serious complications. Three months after ILCP, the mean international prostate symptom score (I-PSS) quality of life (QOL) index and post-void residual volume (PVR) decreased significantly from 18.0 to 9.2, from 4.4 to 2.1 and from 103.6 ml to 44.5 ml, respectively. The mean maximum flow rate (MFR) increased from 7.6 ml/sec at baseline to 9.2 ml/sec 3 months after ILCP, but the difference was not statistically significant. Before and after ILCP, 8 patients were available to evaluate pressure-flow study data. The detrusor pressure at the maximum flow rate decreased significantly from 118.3 cmH2O at baseline to 78.6 cmH2O 3 months after ILCP. The improvement of the I-PSS, QOL index, MFR and PVR continued and at 24 months reached 5.7, 1.8, 11.6 ml/sec and 54.6 ml, respectively. In our assessment of the questionnaire addressing the patient's satisfaction after the treatment, the majority of the patients who answered the questionnaire were pleased with the results of ILCP. We assessed the relation of the overall treatment efficacy with the number of punctures and the total amount of the laser energy delivered, but we did not find any relation. Our clinical results suggest that the ILCP using Indigo 830j is an effective modality and the short-term treatment efficacy is favorable.