Incidence data from the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute, earlier incidence surveys, and the International Agency for Research on Cancer, mortality data from the National Center for Health Statistics, and population data from the Census Bureau were used to assess rates of non-Hodgkin's lymphoma. Mortality and incidence rates have been increasing for many years. Larger increases among older persons suggest a role for improving diagnosis, particularly during the 1950s and 1960s. Urban/rural and socioeconomic differences have diminished over time. Since the early 1970s, incidence rates increased at 3-4%/year, more rapidly than for all other cancers except melanoma of the skin and lung cancer among women. Incidence rates increased over all ages except the very young, among whites and blacks, in geographic areas both in the United States and internationally, and both sexes. During the 1980s, the impact of AIDS is apparent among young and middle-aged men. Differences in non-Hodgkin's lymphoma rates persist between races and sexes. Increases have been more marked for extranodal disease, particularly those arising in the brain, and for high-grade tumors. Explanations accounting for all the increases in rates are not readily available.