Increasing evidence points to a heritable contribution in the development of lymphoma. The goal of this study was to determine the rate of familial lymphoproliferative malignancy among consecutive lymphoma patients presenting to a tertiary care center and to enrol families with multiple affected first-degree relatives on a data and tissue collection study. Beginning in 2004 all new patients presenting to the Dana-Farber Cancer Institute with non-Hodgkin (NHL) or Hodgkin lymphoma (HL) or chronic lymphocytic leukaemia (CLL) were asked to complete a one-page self-administered family history questionnaire. 55·4% of 1948 evaluable patients reported a first-degree relative with a malignancy, with the highest rate among CLL probands. Lymphoid malignancies were particularly common, with 9·4% of all probands reporting a first-degree relative with a related lymphoproliferative disorder (LPD). This frequency was again highest for CLL, at 13·3% of CLL probands, compared to 8·8% of NHL probands and 5·9% of HL probands (P = 0·002). The prevalence of CLL was significantly increased in parents of CLL probands (P < 0·05), and a greater risk of NHL was seen in fathers of NHL probands than in mothers (P = 0·026). We conclude that familial aggregation of LPDs is common among newly diagnosed patients, varies significantly by diagnosis and contributes meaningfully to the population disease burden.