OBJECTIVE We describe long-term results of transurethral microwave thermotherapy. We determined pretreatment variables favorable for the outcome. METHODS We followed for 4 years 187 patients treated with Prostatron software 2.0.* Preoperative evaluations consisted of score, cystoscopy, transrectal ultrasonography, urine flow and residual volume measurements. Followup examinations with score and urodynamics were performed for 4 years after transurethral microwave thermotherapy. Kaplan-Meier plots and logistic regression were used for statistical analyses. RESULTS A decrease in the number of satisfied patients was noted from 62% at 1 year after transurethral microwave thermotherapy to 23% at 4 years. Initial decrease in score and increase in urine flow were followed by increase in score and decrease in flow at the 4-year followup of the 56 patients who had not received supplementary benign prostatic hyperplasia (BPH) treatment. The Kaplan-Meier analysis estimated the median time for need of supplementary BPH treatment to be 45 months. Pretreatment urine flow greater than 10 ml. per second and an irritative score less than 5 were the only factors related to a favorable outcome. Prostate volume or energy delivered to the prostate did not influence the result. CONCLUSIONS Four years after transurethral microwave thermotherapy 23% of the initially treated group were satisfied with the result. Two-thirds had received supplementary BPH treatment. Preoperatively less obstructed patients and those with low initial irritative scores responded more favorably to transurethral microwave thermotherapy treatment.