Three hundred Japanese patients with benign prostatic hyperplasia (BPH) who started an alpha1-adrenoceptor blocker, tamsulosin, between 1993 and 1996 were followed for 3.0+/-3.3 years (mean+/-SD) to determine whether an association existed between the disease severities measured prior to the tamsulosin treatment and the timing at which the invasive therapy was implemented. Patients with a lower quality of life (QOL) index or maximum urinary flow rate (Qmax) were transferred for invasive therapy earlier than those with less severe BPH. The International Prostate Symptom Score (I-PSS) was also associated, but apparently to a lesser extent, with the timing of the invasive therapy. Finally, the overall severity evaluated using all of the above three indices, I-PSS, QOL index, and Qmax, in accordance with the 'Severity Criteria for BPH' issued by the Japanese Urological Association, was found to be a good measure for predicting the prognosis of patients with BPH treated with tamsulosin.