To evaluate the efficacy and long-term benefits of tamsulosin in the treatment of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS). A total of 100 men diagnosed with CP/CPPS were randomly allocated to receive either 0.2 mg of tamsulosin daily or placebo for 6 months. Patients were followed up at 3, 6, 12, 18 and 30 months after initiation of treatment. The primary outcome variable was the change from baseline in the total and domain scores of the NIH-CPSI. Secondary variables used to evaluate efficacy of treatment included the following: peak urinary flow rate, post-voiding residual (PVR) volume and the International Index of Erectile Function (IIEF). The tamsulosin patients had modest satisfactory improvements compared to the placebo group during treatment. Six months after initiation of treatment, the mean decrement of total NIH-CPSI score in tamsulosin and placebo group were 7.5 +/- A 1.9 and 4.0 +/- A 2.3, respectively, P < 0.01. After cessation of therapy, the significant difference waned gradually. Two years after cessation of therapy, the mean decrement of total NIH-CPSI score in two groups were 3.0 +/- A 1.3 and 1.9 +/- A 0.9, respectively, P > 0.05. No differences were observed for data of patients classified as class III A or III B and data of peak urinary flow rate, PVR and the IIEF during the study period. Our study shows that a 6-month course of tamsulosin ameliorated symptoms of CP/CPPS during treatment. However, these effects decreased gradually 6 months after cessation of treatment. This suggests that long-term tamsulosin may be indicated, particularly in the responders.