Because the effects of changing technology in percutaneous transluminal coronary angioplasty, increased operator experience and use of the procedure in patients with extensive disease are unknown in regard to complication patterns, the initial 1977-1981 cohort and the recent 1985-1986 cohort of the National Heart, Lung, and Blood Institute Percutaneous Transluminal Coronary Angioplasty Registry were analyzed with respect to complications. Compared with the initial cohort of 1,155 patients, the 1,801 new cohort patients were older and had an increased prevalence of multivessel coronary artery disease, depressed left ventricular function and prior infarction. Overall complication rates in the recent cohort were either unchanged or decreased from the rates in the initial cohort despite a higher risk patient population. The most significant decreases were in the incidence of coronary spasm (p less than 0.001) and the need for emergency coronary bypass surgery (p less than 0.01). Overall in-hospital mortality was low but was dependent on the extent of vessel disease--0.2% for single vessel disease, 0.9% for double vessel disease and 2.2% for triple vessel disease (p less than 0.001 for linear trend). Acute coronary complications of branch occlusion, dissection or abrupt closure were associated with increased rates of death, nonfatal infarction or need for emergency surgery. Factors showing a multivariate association with increased mortality included a history of congestive heart failure (p less than 0.001), age greater than or equal to 65 years (p less than 0.01), triple vessel or left main coronary artery disease (p less than 0.05), female gender (p less than 0.05) and new onset angina.(ABSTRACT TRUNCATED AT 250 WORDS)