We analysed the risk of cutaneous malignant melanoma (CM) occurring in patients following a diagnosis of non-Hodgkin's lymphoma (NHL) or chronic lymphatic leukaemia (CLL), and of NHL or CLL subsequently developing in CM survivors. Cohorts of patients with CM, NHL or CLL (index cancer) diagnosed between 1975 and 1997 were identified from the Scottish national cancer registry and followed through the registry for subsequent CM, NHL or CLL. The standardised incidence ratio (SIR) for each cancer was calculated and overall risk, risk in relation to gender and age at diagnosis of the index cancers and time from diagnosis of the index cancer to the diagnosis of the second malignancy were measured. There were 9385 CM patients, 4016 CLL patients and 13 857 NHL patients identified with an index cancer with 56 195, 14 450 and 44 999 person-years of follow-up, respectively. There was an increased risk of both CLL and NHL following a diagnosis of CM (SIR 2.3 and 1.5, respectively) and of CM following a diagnosis of CLL and NHL (SIR 2.3 and 2.1, respectively). The risk was statistically significantly increased for CLL developing in CM patients and for CM occurring in NHL survivors (P<0.05). This study supports an association between CM, CLL and NHL developing in the same patient. Immunosuppression, exposure to ultraviolet radiation and genetic factors may lead to a host environment that is conducive to the development of these malignancies.