We describe pronounced hypotension in a patient during orthostatic testing while receiving treatment with sildenafil and tamsulosin, but not with placebo. The patient was 71 years of age and had no history of orthostatic reactions. He had been diagnosed with benign prostatic hyperplasia (BPH) and glaucoma simplex (open-angle glaucoma). The only regular medication used was a combination of latanoprost and timolol one drop daily into each eye. The patient was among 16 men with BPH enrolled in a study of the haemodynamic effects of tamsulosin and sildenafil. The present patient was excluded from data analysis because of atypical reactions: he experienced a decrease in peripheral vascular resistance upon orthostasis during treatment with sildenafil and tamsulosin. This led to marked hypotension and cancellation of the tilt tests with both sildenafil alone (Riva-Rocci [RR] 75/50 mm Hg) and a combination of sildenafil and tamsulosin (RR 60/45 mm Hg); however, tamsulosin alone also lowered blood pressure to some extent (RR 100/80 mm Hg). In conclusion, even though sildenafil and tamsulosin are considered haemodynamically safe, they may induce considerable vasodilation and, subsequently, harmful hypotension in susceptible patients.