For a single year, 1983, we compared the actual and estimated morbidity, mortality, and costs attributable to measles, mumps, and rubella with having or not having a childhood immunization program using the combined measles-mumps-rubella (MMR) vaccine. Without an immunization program, an estimated 3,325,000 cases of measles would occur as compared to 2,872 actual cases in 1983 with a program. Instead of an expected 1.5 million rubella cases annually, there were only 3,816 actual cases. Mumps cases were lowered from an expected 2.1 million to 32,850 actual cases. Comparable reductions in disease-associated complications, sequelae, and deaths are gained with an immunization program. Without a vaccination program, disease costs would have been almost $1.4 billion. Based on the actual incidence of disease in 1983, costs were estimated to be approximately +14.5 million. Expenditures for immunization, including vaccine administration costs and the costs associated with vaccine reactions, totaled $96 million. The resulting benefit-cost ratio for the MMR immunization program is approximately 14:1. The savings realized due to the use of combination rather than single antigen vaccine total nearly $60 million.