To investigate whether a history of hematolymphoproliferative cancers (HLP) and other cancers among a parent or sibling is a risk factor for specific subtypes of leukemia and non-Hodgkin's lymphoma (NHL), data from a population-based case-control study, in Iowa and Minnesota, of 578 leukemia cases, 622 NHL cases and 1245 controls were evaluated. Having at least one sibling with HLP significantly increased the risk for all leukemias combined (odds ratio (OR) = 2.3) and for NHL (OR = 2.7). In particular, chronic lymphocytic leukemia (CLL) was significantly increased among those reporting a sibling with leukemia (OR = 3.0) or lymphoma (OR = 4.3). Elevated risks of small lymphocytic NHL (SML) (OR = 7.3) and diffuse NHL (DIF) (OR = 5.4) were also observed among subjects who had a sibling with lymphoma (primarily Hodgkin's disease). A significantly increased risk of follicular NHL was noted among those with a sibling history of pancreatic cancer (OR = 4.8) and colorectal cancer (OR = 2.7). Parental history of HLP was not associated with any type of leukemia or NHL. A history of stomach cancer among parents was associated with a 2-fold elevation of CLL and DIF compared to controls. Increased risks of CLL and DIF were also linked to breast cancer among sisters and mothers, respectively. Prostate cancer among fathers increased the risk 2-fold for CLL and 3-fold for SML. This study confirms some familial cancer associations previously reported for leukemia and NHL, and provides new information regarding the various subtypes of leukemia and NHL.