OBJECTIVES To study risk factors for acute myocardial infarction (AMI) in men suffering from benign prostatic hypertrophy. METHODS We followed 811 patients who underwent transurethral resection of the prostate (TURP) between 1983 and 1992 until the end of 1993 with regard to the incidence of AMI. The association between AMI and various potential risk factors was evaluated by epidemiological methods. RESULTS Fifty-two patients developed a first-time AMI after TURP. A pre-operative blood haemoglobin concentration in the range of 100-129 g/l (normal range 130-165 g/l) was associated with an increased long-term relative risk of a first-time AMI, which was estimated to be 2.0 (95% confidence interval = 1.0-4.1). This estimate became slightly stronger when we also included the 76 patients with a first AMI before surgery, 10 of whom developed a re-infarction after TURP. Furthermore, it was largely unchanged on adjusting for impaired health status and age > or = 75 years (patient factors) and for fluid absorption > or = 500 ml and a blood loss > or = 275 ml (operative factors), which had been reported to increase the long-term risk of AMI in a previous study. CONCLUSION A moderately reduced blood haemoglobin level before TURP is associated with a doubled risk of developing AMI in later life.