The aim of the present study was to elucidate the clinical characteristics of pregnancy-associated maternal deaths.We performed a retrospective analysis with medical records and autopsy reports of cases of pregnancy-associated deaths. We collected information on all maternal deaths related to pregnancy that occurred in 3 hospitals affiliated with Nippon Medical School in Japan from January 1, 1984, to December 31, 2014. Data analyzed were maternal age, past medical history, parity, gestational age, clinical signs and symptoms, cause of death, and maternal autopsy findings.A total of 26 maternal deaths occurred during the 31-year study period. Autopsies were performed for 16 patients (61.5%). The 26 deaths included 19 (73.1%) classified as direct maternal deaths and 7 (26.9%) classified as indirect maternal deaths. The mean maternal age at death was 33.1±4.3 years (range, 26-41 years). The highest percentage of women was aged 35 to 39 years (38.5%). Of the 26 maternal deaths, 69% occurred at 32 to 41 weeks of gestation. In cases of direct maternal death, the leading causes were amniotic fluid embolism (7 cases, 27.0% of all deaths) and hemorrhage (6 cases, 23.1% of all deaths). In cases of indirect obstetric deaths, the causes included cardiovascular disorders, cerebrovascular disorders, sepsis due to group A streptococcal infection, and hepatic failure of unknown etiology.Amniotic fluid embolism was the leading cause of maternal deaths and was followed by obstetric hemorrhage. To prevent and reduce the number of maternal deaths in Japan, further basic and clinical research on amniotic fluid embolism is required.