The impact, time trends and potential for prevention of premature deaths in Canada were assessed. There were almost 100,000 deaths before age 75 in Canada during 1986 resulting in over 1.7 million potential years of life lost (PYLL). The three leading broad disease categories responsible for PYLL were cancer, injuries/violence and cardiovascular disease. In both sexes, coronary heart disease, car accidents, lung cancer and perinatal conditions ranked in the top 5 specific diseases responsible for PYLL; breast cancer (females) and suicide (males) also ranked in the top 5 conditions. Over the period 1969 to 1986, death rates among persons less than age 75 increased for 3 conditions among females and 11 conditions among males. Lung cancer and brain cancer death rates increased in both sexes, chronic obstructive pulmonary disease death rates increased among females only and death rates for suicide and 8 types of cancer increased among males only. Over the same period, death rates declined for 37 discrete disease categories among both females and males including particularly large improvements for coronary heart disease, stroke, car accidents and perinatal conditions. An estimated 50,000 or over 50% of all premature deaths per year are preventable through control of smoking, hypertension, elevated serum cholesterol, diabetes and alcohol abuse. About 6,000 premature deaths are avoidable through improvements in medical care.