Several case-control studies have demonstrated positive associations between parental occupational exposures and childhood cancer. However, an overestimation of risk estimates due to recall bias is of concern. The magnitude and nature of this bias were explored using data from a German case-control study on childhood leukemia conducted between 1992 and 1997. A moderate overreporting of occupational exposures by fathers was observed, particularly for the prenatal period. Overreporting was most apparent when the time between exposure and interview was short. It was also found that job titles were no satisfactory substitute for information on specific occupational exposures. The results of this analysis emphasize the need for more sophisticated exposure assessment methods in epidemiologic studies of childhood cancer. However, because future case-control studies will at least partially rely on questionnaire data, improvements including probing questions, better interview techniques, and validation studies are indicated.