From January 1983 through December 1987, 98 patients underwent angioplasty of at least one diffusely diseased coronary artery. Diffuse coronary disease was described as: group I, narrowing greater than or equal to 50% that involved the entire vessel (40 patients), group II, long lesions greater than or equal to 2 cm in length (39 patients), group III, three or more lesions in the same vessel (19 patients). There were 65 men and 33 women, with a mean age of 60 years; 64 patients (65%) had unstable angina, 23 patients (23%) were diabetic, 31 (32%) had prior myocardial infarctions, and 12 had prior bypass surgery. Multivessel disease was present in 89% of patients. Angioplasty of only the diffusely diseased vessel was performed in 41 patients, and additional vessels were dilated in 57 patients. Overall, of 396 lesions (four per patient) and 197 vessels (two per patient) attempted, success was achieved in 382 lesions (96%) and 187 vessels (95%); angiographic success was achieved in 112 of 120 diffusely diseased vessels (93%). Clinical success was achieved in 91 patients (93%). The overall complication rate (death, myocardial infarction, urgent bypass surgery) was 8% (8 of 98): six patients (6%) had myocardial infarction (one Q wave, five non-Q wave), one patient (1%) had urgent bypass surgery, and two patients (2%) died (one during bypass surgery). The majority of complications (7 of 8 or 87%), including the two deaths, occurred in group I patients, with a 17.5% rate, versus 2.5% in group II and 0% in group III, p less than 0.002.(ABSTRACT TRUNCATED AT 250 WORDS)