The characteristics of multiple primary carcinomas associated with thyroid carcinoma were studied in 35 patients (35/362; 9.7%) who met the clinicopathological criteria of Warren and Gate. The frequency of the association was similar in papillary and follicular thyroid carcinomas. The average patient age at the time of initial carcinoma detection was 60.3 years for males and 51.5 years for females. The most frequent sites of the associated cancers were breast, uterine cervix and uterine body in females, and stomach and larynx in males. Patients should be followed closely for recurrence and second cancer detection in the early stage.