Nine patients with radiologically proven vesicorenal reflux (3 bilateral, 4 unilateral, 2 with unilateral double-J stents) received intravesical bacillus Calmette-Guérin (BCG) as prophylactic treatment for recurrent superficial bladder carcinoma. One patient with a double-J stent suffered an attack of high fever, probably following obstruction of the stent. All other patients tolerated one cycle or two cycles (5 of 9 patients) of 6 weekly instillations without significant complications. There was no increased toxicity compared with a control group of 39 patients without reflux who were receiving BCG. Topical intravesical immunotherapy with BCG in patients with vesicorenal reflux can be given without a rise in the complication rate; indeed, in view of the multifocal appearance of urothelial carcinoma in this subgroup, this type of therapy even appears to be desirable.