Organochlorines have been linked with non-Hodgkin's lymphoma (NHL) in epidemiological studies. We elucidate the importance of hexachlorocyclohexane (HCH), an organochlorine insecticide, in the aetiology of NHL among individuals with dermal exposure to HCH. This is a case-control study nested in a cohort of sheep owners, collected from records on sheep dipping. The number of dipped sheep was used as surrogate for exposure. No other insecticide was used in sheep dip in Iceland during the study period. Cases (n=45) were identified by record linkage with the national cancer registry (through 1962-2003) and controls (n=221) were selected at random from the cohort. In logistic regression analysis the odds ratio for NHL was 3.86 (95% CI 1.59-8.53), adjusted for age, for individuals who had 100 sheep or more as compared to those who had less than 100 sheep. The results indicate that HCH may be linked to the development of NHL.