OBJECTIVES: Data from a hospital based case-control study were analysed to assess the relation between maternal occupation in the leather industry and several groups of congenital defects (nervous system, cardiac defects of closure, oral cleft, epispadia or hypospadia, and multiple anomalies). METHODS: Cases and controls were selected from eight public hospitals in Comunidad Valenciana, Spain, in 1993 and 1994. Cases were located from the hospital discharge records, including children born and diagnosed in some of the selected hospitals during their first year of life. Controls were selected from births without congenital defects in the same hospitals and dates of the cases (ratio 1:1). Both parents of selected children were interviewed (mainly by phone) and information about potential confounding variables and occupational history during the three years before the birth was collected in structured questionnaires. RESULTS: A total of 261 cases and the same number of controls were included in the study. Adjusted odds ratios (ORs) were estimated for maternal occupation in the leather industry in the period between three months before the conception and the birth of the child (n = 22), and each selected group of congenital malformations: nervous system defects (OR 1.02, 95% confidence interval (95% CI) 0.12 to 8.51), cardiac defects of closure (OR 1.78, 95% CI 0.44 to 7.17), oral clefts (OR 6.18, 95% CI 1.48 to 25.69), for epispadia or hypospadia (OR 4.05, 95% CI 0.77 to 21.44), and multiple anomalies (OR 3.14, 95% CI 0.82 to 12.00). CONCLUSION: These data are compatible with an increased risk for oral clefts in the offspring of women working in the leather industry. Some other categories of defect could have an increased risk as well, although for these our data cannot exclude random error as an explanation. Given these results and previous findings in similar studies, some precautionary recommendations regarding maternal exposure in leather industries, probably in relation to solvents, would be justified.