Some epidemiological aspects of Paget's disease were examined using questionnaires completed by 864 patients with physician-diagnosed Paget's disease and 500 controls of similar ages. Specifically studied were issues of familial aggregation of the disorder, history of exposure to certain infectious diseases, other medical disorders, and calcium intake (as assessed by milk consumption) in childhood. A history of Paget's disease in a first-degree relative was noted in 12% of patients and 2% of controls. Among patients, those with a positive family history had an earlier mean age at diagnosis and a greater prevalence of bone deformity than patients with a negative family history. The risk of a first-degree relative of a pagetic patient developing Paget's disease was 7 times greater than the risk of an individual without such a relative, and the cumulative risk to age 90 for a first-degree relative of a patient was 9%, compared with a 2% risk in a person without affected relatives. The risk to the relative was greatest if the patient had an age at diagnosis of less than 55 years and had deforming bone disease. There was no difference between patients and controls for a variety of viral infections, including measles, and no difference in ownership of dogs and possible exposure to canine viruses. Diabetes was more common in controls than in patients, but arthritis, skeletal fractures, primary hyperparathyroidism, osteoporosis, and thyroid disease (in women) and renal stones (in men) were reported more commonly by patients. Milk consumption during childhood and adolescence was lower in patients than in controls.(ABSTRACT TRUNCATED AT 250 WORDS)