Objective. To evaluate the efficacy of the selective alpha-blocker tamsulosin on stone clearance after shockwave lithotripsy (SWL) of renal stones. Material and methods. A prospective, randomized, controlled study was carried out in 166 patients who underwent SWL for renal stones between January and December 2007. Group 1 (n = 83) took tamsulosin 0.4 mg once daily and diclofenac sodium injection (75 mg) on demand. Group 2 (n = 83) took only diclofenac sodium as needed. Patients were on this regimen for 4 weeks or until stone clearance and were followed up for a maximum of 3 months. They were evaluated for stone clearance, time to stone clearance, colic attacks, need for analgesics and any side-effects at 2 weeks, and 1, 2 and 3 months. Results. In total, 136 patients (67 in group 1 and 69 in group 2) were available for evaluation. The demographic profile was comparable in both groups. Group 1 had a clearance rate of 73% (49/67) versus 55% (38/69) in group 2 (p = 0.008). Time to stone clearance was significantly different at 1, 2 and 3 months (p = 0.02, 0.01 and 0.008, respectively), but not significant at 2 weeks (p = 0.52). In group 2, higher number of patients had more frequent attacks of colic and used more analgesics than in group 1 (p = 003, 0.001 and 0.002, respectively). Nine patients (13.4%) in group 1 had ejaculatory dysfunction. Conclusions. Tamsulosin significantly increases stone clearance after SWL of renal stones. It decreases the pain and amount of analgesics needed, with a low rate of side-effects.