Extremely low frequency magnetic fields (ELF-MFs) have been classified as possibly carcinogenic to humans by the International Agency for Research on Cancer. The authors investigated, in a population-based case-control study in Germany, if children whose parents were exposed preconceptionally at work to ELF-MFs had an increased risk of developing cancer. Cases aged 0-14 years were ascertained from the German Childhood Cancer Registry. Controls were selected from local resident registration offices. The parental occupational history was recorded in questionnaires and telephone interviews, and preconceptional magnetic field exposure was estimated according to a job-exposure matrix. The analysis included 2,382 controls and 2,049 cases (846 children with acute leukemia, 159 children with non-Hodgkin's lymphoma, 444 children with central nervous system tumors, and 600 children with other solid tumors). Frequency-matched conditional logistic regression models revealed no increased cancer risks in children whose fathers were occupationally exposed to magnetic fields above 0.2 microT. Additionally, there was no evidence for a risk increase at magnetic field levels exceeding 1 microT. Based on much smaller numbers, maternal occupational exposure was also not related to increased cancer risks. In this large case-control study, the risk of childhood cancer was not linked to preconceptional parental ELF-MF exposure.