To identify ways in which the safety of childbirth might be increased, we investigated the causes of death among the 886 women who died during pregnancy or within 90 days post partum ("maternal deaths") in Massachusetts from 1954 through 1985. The maternal mortality rate declined from 50 per 100,000 live births in the early 1950s to the current rate of 10 per 100,000 live births. Between one third and one half of the maternal deaths were considered to have been preventable. The leading causes of maternal death from 1954 through 1957 were infection, cardiac disease, pregnancy-induced hypertension, and hemorrhage. In contrast, from 1982 through 1985 the leading causes of death were trauma (suicide, homicide, and motor vehicle accidents) and pulmonary embolus. We observed a rapid increase in the frequency of death among women who received little or no antenatal care. From 1980 through 1984 the maternal mortality rate for white women was 9.6 per 100,000 live births, whereas for nonwhites it was 35 per 100,000 live births (relative risk, 2.9; 95 percent confidence limits, 2.5 and 3.2). Fifty percent of the nonwhite women who died during pregnancy or within 90 days post partum received little or no antenatal care, in contrast to only 15 percent of the white women. These data show that the leading causes of maternal death have changed markedly in Massachusetts during the past 30 years. Although the overall maternal mortality rate has declined sharply, further improvement may occur with better antenatal care and specific efforts to prevent trauma and pulmonary embolus.