The objectives of this study are: 1) To evaluate the hypothesis that risk of Hodgkin's disease is a function of factors in childhood environment which inhibit infectious transmission: in particular, family size, birth order and social class. 2) To re-evaluate the association of tonsillectomy and risk of Hodgkin's disease. 3) To evaluate occupational exposures and risk of Hodgkin's disease. 4) To establish a serum bank. In part I of the study, conducted in the Boston and Worcester metropolitan areas, essentially all incident cases of 54 month period will be identified. Controls will include siblings of cases as well as persons selected by a random process from the general population. Information will be gathered by home interview; blood specimens will be obtained from cases and sibling-controls. Part II will be conducted by mail questionnaire in the Detroit metropolitan area. A similar case series will be identified and their siblings used as controls.