Nineteen dogs with vesico-urethral reflex dyssynergia (VURD) were treated with prazosin or terazosin 0.5 mg/kg twice daily to compare efficacy and side effects. Dogs were referred because of signs of (partial) urethral obstruction. Physical examination, abdominal ultrasonography, urinalysis and a radiographic contrast study of bladder and urethra (urethrocystography) were routinely performed. If no mechanical causes of obstruction or disease of the distal urinary tract were observed, the diagnosis VURD was presumed and the dogs were included in our study. Follow-up information was obtained from owners or referring veterinarians. Significantly more side effects were seen in the dogs treated with terazosin (n=14; 93 per cent) compared with the dogs treated with prazosin (n=5; 20 per cent; P=0.002). Effects of the treatment were comparable between prazosin and terazosin. Labradors and dogs that were castrated surgically had a significant better survival (P<0.01) compared with other breeds and animals that were castrated chemically. There was a moderate to good effect in 60 per cent of the dogs treated with prazosin, and in 64 per cent of the dogs treated with terazosin.