The relation of occupation to the risk of testicular cancer was investigated in a case-control study using data from the files of the South Thames Cancer Registry. Risks by age and histology subdivisions of the tumour were investigated since there is epidemiological evidence of differences in aetiology between these subdivisions but no previous systematic study of occupational risks by age and histology. Analyses were conducted comparing 1605 cases of testicular cancer incident in the region during 1958-77 with 7187 controls selected from other cancers incident in men in the region during the same period. The greatest risks of testicular cancer overall were for administrators and managers, sales workers, professional and allied workers, electrical workers, and clerical workers; these occupations were generally also at high risk of subdivisions of the tumour age and histology. Risk of testicular cancer overall and in each age and histology subgroup was greater in men of high than of low occupation based social class. Occupations with high risk of testicular cancer for their social class are of particular interest for further investigation of possible occupational risk factors; occupations with this characteristic for testicular cancer overall or in subdivisions in the present and some previous data are farmers, electrical workers, and paper and printing workers.