Purpose: We attempted to identify any parameter that could possibly lead to a successful treatment outcome after transurethral microwave thermotherapy. Materials and Methods: Clinical parameters and treatment profiles of 292 patients were analyzed in a retrospective multicenter manner. Responder and nonresponder groups were identified according to a given definition. Results: No statistically significant differences in baseline characteristics were found. Responders showed a 76% symptomatic improvement rate compared to 27% in nonresponders, and an 82% improvement rate in peak flow compared to a 5% decrease in nonresponders. Responders also showed a significantly greater increase in posttreatment PSA level and a significantly greater amount of energy released during treatment. Conclusions: No baseline clinical parameter is capable of predicting treatment outcome.