A prognostic index based on admission characteristics of patients with inferior acute myocardial infarction was developed to predict mortality and other major complications during hospitalization. The study sample included 1841 consecutive patients with a first inferior wall acute myocardial infarction, hospitalized in 13 out of 21 operating coronary care units in Israel. Age, angina in the past, congestive heart failure and blood glucose level > 180 mg/dl were independently associated with higher in-hospital mortality and morbidity. The prognostic weights of these risk factors were determined in a study group which comprised two thirds of the patients (n = 1210) who were randomly selected from the 1841 participants. A prognostic score (range, 0-15) was calculated as the sum of the prognostic weights of the above four risk factors for each patient. These scores were determined in both the study group and in a validation group (the remaining one third of the patients, n = 592). In-hospital mortality in the study group ranged from no death for 102 patients with a prognostic score of 0, to a 37% mortality rate in 106 patients whose prognostic score was > 8. Accordingly, the study group was divided into groups of low-risk (score 0-5), intermediate-risk (score 6-8) and high-risk (score > 8), with in-hospital mortality of 3, 13 and 37%, respectively. In-hospital mortality among patients in the validation group determined to be at low-, intermediate- and high-risk was 3, 13 and 44%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)