In a representative series of male patients (n = 504) surviving the hospital stay of a first myocardial infarction the prevalence of hypertension and the influence of hypertension on the prognosis during 2 yr follow-up were studied. According to the definitions used hypertension had been detected before or was detected after myocardial infarction in 36% of the patients. Two thirds had a history of hypertension known before infarction. The systolic and diastolic blood pressures measured at 3 months and 1 yr after infarction increased with age. There was no difference between patients with and without hypertension with respect to a number of different variables recorded during the hospital period, nor in multiple risk according to a logistic function. There was no difference in death rate between the two groups. However, the rate of non-fatal reinfarction was significantly higher among the hypertensive patients. Hypertension remained as a risk factor for after myocardial infarction when the possible confounding influences of serum lipid levels and tobacco smoking were analysed.