A case control study of parental occupation and childhood brain tumor risk was conducted. The cohort consisted of 110 cases of primary brain cancer occurring in patients under 20 years of age between 1 January 1975 and 31 December 1982. The cases were identified from the Columbus, Ohio, Children's Hospital Tumor Registry. The referents consisted of 193 cancer free persons living in surrounding counties who were matched to the cohort by age, sex, and race. The biological parents of the subjects were interviewed to obtain information on parental occupation and industry during the preconception, pregnancy, and postnatal periods. The preconception period was defined as the year preceding conception and the postnatal period as the period from birth to time of diagnosis. Attempts were made to assess occupational exposures to organonitrogen compounds and other agents. Odds ratios (ORs) for brain cancer risk were computed. Paternal employment in agriculture, construction, metal, food, and tobacco industries and in farming, benchwork, and transportation jobs were associated with an increased risk of childhood brain cancer, ORs 2.0 to 3.3. The greatest risk was associated with the preconception period. Few associations were obtained for maternal employment. Only one occupation, processing, had an elevated risk, OR 2.6. Job clusters having moderate to heavy exposures to aromatic and aliphatic hydrocarbons, aromatic amines, and nonionizing radiation were associated with an increased risk. Paternal exposures to aromatic amines and aromatic nitro compounds especially during the postnatal period were associated with an increased risk, ORs 3.4 to 4.4. The authors conclude that the study data indicate that paternal exposure just before conception appears to present the highest risk for childhood brain cancer. The data do not conclusively prove that paternal occupational exposures cause childhood central nervous system tumors but they are consistent with the hypothesis that paternal germ cell damage may manifest itself years later as cancer in the offspring.