OBJECTIVES: A case-control study was carried out to explore associations between spina bifida and occupational exposure of the mother. METHODS: The cases were children with spina bifida aperta born between 1980 and 1992 from nine hospitals in the Netherlands. The controls were children born healthy in the same period as the cases, from hospitals and from the general population. Data collection was carried out in two steps. Firstly, postal questionnaires were sent to all the parents of cases and controls to gather information on occupations and potential confounders. In the second phase of the study, information on specific exposures was collected by means of job and task specific personal interviews. Interviews were performed with 55 case mothers and 66 control mothers who had occupations with a potential for chemical or physical exposure. Those exposures were assumed to be negligible for--for example, teachers and secretaries, so personal interviews were not indicated for these women. Information was collected on specific tasks in the period just after conception, and on the associated use of chemical or physical agents, frequency of exposure, and use of protective equipment. RESULTS: The analyses of occupation showed an increased risk for women working in agricultural occupations (OR = 3.4, CI:1.3-9.0), and, although less distinct, for cleaning women (OR = 1.7, CI:0.9-3.4). Only a few women seemed to be occupationally exposed to chemical or physical agents. No differences in occurrence of specific exposures could be detected between cases and controls. Besides, no differences were seen in pesticide or disinfectant exposure among case and control mothers in agricultural occupations. CONCLUSIONS: Occupational exposures of the mother during pregnancy were infrequent and did not seem to play an important part in the aetiology of spina bifida in this study. The association found between spina bifida and maternal agricultural occupations could not be explained by the use of pesticides by the mother or by any other occupational exposure.