This report examines trends in the number and the rates of coronary artery bypass surgery (CABS) in Canada, performed over a six-year period from 1981-82 to 1986-87. The analysis includes comparisons of rates and events by sex, age and geographic location. In Canada 10,865 CABS were performed in 1986-87 representing a 39% increase over 1981-82. During the same period the rate of CABS rose to 43.2 per 100,000 population. In the twelve census metropolitan areas (CMAs) covered in this study, CABS increased 45.7% from 6,477 in 1981-82 to 9,439 in 1986-87, while hospital separations for Ischemic Heart Disease (IHD) increased by 22.6%. Regionally the coronary artery bypass surgery rate was lowest in Halifax at 62.4 per 100,000 population and highest in Ottawa-Hull at 131.8 per 100,000 population. The average annual proportion of CMAs ranged from 15.5% for residents in Halifax (84.5% for non-residents) to a high of 65.7% for residents in Montreal (34.3% for non-residents). Procedure rates increased consistently among the 65-74 and 75+ age groups, remained stable in the 55-64 age group, and decreased in the 35-54 age group. The variations among the CMAs may in part be due to the amount of resources available in each CMA, the demand for this type of service and perhaps to differing patterns of physician practice.