We report the results of a hospital-based, case-control study on acute lymphocytic leukemia (ALL), acute non-lymphocytic leukemia (AnLL) and non-Hodgkin lymphoma (NHL) in childhood. The study was conducted from 1981 to 1984 in Turin (Italy). One hundred and forty-two children with ALL, 22 with AnLL and 19 with NHL were included, as well as 307 controls. Information on parental smoking habits, parental occupation, ionizing radiation and childhood diseases were collected using a standard questionnaire during a personal interview of the relative attending the child in the hospital. The odds ratios for antenatal diagnostic radiation were 1.1 (NS) for ALL and 2.4 (NS) for AnLL. No association was found with diseases in childhood. Paternal and maternal smoking habits were similar for ALL cases and controls. Both maternal and paternal smoking were associated with NHL: for paternal smoking, odds ratios were around 5, but without a correlation with number of cigarettes. Positive associations observed with maternal employment were: ALL with teacher and cleaner; AnLL and textile worker; NHL and baker. Corresponding association with paternal jobs were: ALL with clerks, farmers and employment in office equipment production; AnLL and workers in building, tire or textile industries; NHL and lorry drivers, workers in the building or in the wood and furniture industry.