A retrospective review of 287 patients with a diagnosis of adenocarcinoma unknown primary site was performed. These patients represented 2.9% of the new referrals to the Westmead Department of Radiation Oncology between the years 1979 and 1985. Age, sex, and survival characteristics of the study population are presented. Tissue biopsy procedures are reviewed and the uniform necessity of open biopsy is questioned in the light of recent advances in FNA (fine needle aspirate) techniques. A semi-quantitative analysis of the monetary cost of the investigation of these patients has been performed. This has been correlated with the objective and symptomatic benefit accrued by the patient population. A higher incidence of speculative, low-yield investigations has been demonstrated for those patients referred from general medical and surgical units. Ante-mortem identification of the primary site remains the exception rather than the rule in this and other series. This fact, coupled with an inability of therapeutic intervention to alter the natural history of the disease means the cost and toxicity of investigation and treatment of these patients must influence approaches to their management.