A retrospective review of 1539 patients with cancer of unknown primary site seen at Yale-New Haven Hospital from 1922 to 1981 was performed. Information was obtained from the Tumor Registry. The method of diagnosis, patient characteristics, year of diagnosis, histologic features, treatment received, and survival were analyzed. The most common cell type was adenocarcinoma. Survival overall was poor, with a median survival of 5 months for the entire group. Age and year of diagnosis did not appear to significantly influence survival. Closer examination of a small subset of those patients with squamous cell carcinoma revealed a very high male:female ratio, possibly related to tobacco and alcohol abuse. Nearly 9% of these patients were found to have a history of one or more unrelated malignancies.