This paper presents the results of a retrospective study that examines the association of cancer with a history of asthma, hay fever, hives, and other allergy-related diseases. This study is based on interview data collected from 13,665 cancer cases and 4,079 nonneoplastic controls who were admitted to Roswell Park Memorial Institute from 1957 to 1965. Although there is a general tendency for the age- and cigarette smoking-adjusted odds ratios associated with a history of asthma and hay fever to be less than 1, for both males and females, there is stronger evidence for a decreased risk of cancer associated with a history of hives and other allergy-related diseases. Decreased risks associated with a history of hives and other allergies are seen in males for oral cancer, cancers of the lung, larynx, digestive system, urinary system, and cancers of all sites combined and in females for cancers of the digestive system, reproductive system, in particular, cancer of the cervix, and cancers of all sites combined. None of the few odds ratios over 1 associated with a history of any allergy-related condition are statistically significant (alpha = 0.05). These findings suggest that individuals with allergy-related disorders may be at decreased risk of cancer, although reasons for cautious interpretation of the findings are emphasized. Prospective studies of carefully defined allergic disease cohorts are needed.