A case-referent study of birth defects was nested in a prevalence survey of adverse reproductive outcomes carried out among 8867 floriculture workers in Bogotá, Colombia. A total of 535 children born to these workers and reported by their parents as malformed and 1070 children selected at random as referents were invited to a medical examination including consultation with a geneticist and a clinical teratologist and a review of the medical records. Seventy-six percent of both groups attended the examination. Of 403 children reported as malformed, a birth defect was confirmed for only 154 (38%). On the other hand, of the 817 children reported as normal, 735 (90%) were normal, but 68 had a birth defect and 14 had other conditions. A case-referent analysis was then carried out including 222 children with birth defects and 443 referents. An increased risk was found only for birthmarks, and specifically for hemangiomas, for children with parents exposed to pesticides in the floriculture industry.