The relationship between chronic lymphocytic leukaemia (CLL) and primary malignant neoplasms was evaluated using data from the Hematology Division in Beilinson Medical Center and the Israel Cancer Registry. The study population consisted of 81 patients diagnosed between 1962 and 1984. A total of 16 patients were found to have 21 malignant neoplasms in addition to their CLL. Excluding patients with nonmelanoma skin tumours, a 1.7 increased risk (statistically not significant) for developing second malignant neoplasms in CLL patients was detected. The only tumour which occurred significantly more than expected subsequent to CLL diagnosis was brain cancer. The coexistence ofmultiple cancers in the same patient was diagnosed in four ofthe patients. The results of this study further support the hypothesis that patients with CLL are prone to develop second neoplasms.