A study of the incidence of malignant lymphoma in Olmsted County, Minnesota, revealed 91 new cases during the period 1970 through 1977. On the basis of the analyzed data, the overall average annual incidence rate per 100,000 population was 12.2 for males and 14.2 for females. The rates for both sexes combined (unadjusted for age) were 1.5 for Hodgkin's disease, 6.2 for lymphosarcoma, and 5.5 for reticulum cell sarcoma. The incidence rate for Hodgkin's disease decreased insignificantly, whereas that for both lymphosarcoma and reticulum cell sarcoma increased significantly during the period 1970 through 1977 in comparison with rates from the period 1945 through 1969. The largest increase was for rural males, for whom the rates for all three histologic types of lymphoma were substantially higher than those for urban males.