Uterine cancer ranks third in cancer incidence and fifth in cancer mortality among American women. The epidemiologic characteristics of cancer of the cervix uteri and the corpus uteri are different. When only "cancer of the uterus, not otherwise specified (NOS)" is reported, problems arise in data analysis. In this study, uterine cancer deaths from the National Cancer Institute's Surveillance, Epidemiology, and End Results Program, 1977-79, are compared with those from three previous studies. Uterine cancer deaths certified only as uterus, NOS, on death certificates have decreased 34 percent in the past 30 years. However, even in the late seventies, 25 percent of the uterine cancer deaths were still not being specified as either cervix uteri or corpus uteri on death certificates. Following the deaths certified as cancer of uterus, NOS, back to the pertinent hospital records showed that in recent years 75 percent of these deaths were actually diagnosed as cancer of the corpus uteri, compared with 20 percent 30 years ago. The failure to assign these unspecified uterine cancers to corpus uteri indicates that mortality from cancer of the corpus uteri is still underreported. Although the reporting of the specific subsites of cancer of the uterus on death certificates has improved during the past 30 years, every effort should be made to achieve further improvement in accuracy.