A population-based case-control study in Denmark investigated the hypothesis that parental occupation in agriculture increases the risk of testicular cancer in the offspring. Other factors investigated were: childhood residence on a farm, in the country, or in an area with high nitrate concentration in ground water, and the subjects' own occupation in agriculture. The only association that emerged was with childhood residence in the high-nitrate area. The excess risk was, however, confined entirely to men who did not grow up on a farm or in the country. This makes it very unlikely that nitrate exposure per se should be responsible. Further analyses revealed that the excess risk was confined largely to men who grew up in nonrural areas within Arhus County, where Denmark's second largest city is located, and an excess risk was also seen among men who grew up in Copenhagen Municipality, which is the center of the most urban area in Denmark. The geographic pattern of incidence is stronger for the area of childhood residence than for the area of residence at the time of diagnosis. This supports indirectly the idea that testicular cancer is caused by unidentified factors early in life.