Families with multiple individuals affected with chronic lymphocytic leukaemia (CLL) and other related B-cell tumours have been described in the literature. Familial CLL does not appear to differ from sporadic CLL in terms of prognostic markers and clinical outcome. Large, population-based case-control and cohort studies have also shown significant familial aggregation of CLL and related conditions, including non-Hodgkin and Hodgkin lymphoma. Monoclonal B-cell lymphocytosis also aggregates in CLL families. However, the clinical implication of familial aggregation is minimal given the overall rarity of CLL. Linkage studies have been conducted in high-risk CLL families to screen the whole genome for loci that contribute to susceptibility but no gene mutations have yet been identified by this method. Association studies of candidate genes have implicated immune function and other genes but more studies are needed to verify these findings. The ability to conduct large scale genomic studies will play an important role in detecting susceptibility genes for CLL over the next few years and thereby help to delineate aetiological pathways.