Cancer of Unknown Primary Origin (CUPO) is defined by the presence of metastatic lesions, diagnosed by means of cytological or pathological evaluation, for which no primary site can be detected during a thorough examination. The clinical investigation, directed at locating the site of the neoplastic lesion, is determined by the results of laboratory tests, imaging procedures, and pathological examinations. It is also essential to conduct a complete medical history and thorough physical examination. The detection of the primary site allowed to introduce specific therapy, which can offer clinical benefits, considering a favorable prognosis.was to assess the range of diagnostic procedures performed in patients with CUPO and efficacy in identifying the primary lesion.Retrospective analysis comprised a group of 29 patients with CUPO, operated between January, 2002 and December, 2011, at the Department of Surgical Oncology, Medical University in Łódź. The study group comprised 16 male and 13 female patients; median age at presentation was 58.3 years (ranging between 30-79 years).Detailed diagnostic management depending on the location of metastatic lesions and their histological type was performed in 20 of the 29 study patients (69%). Considering the remaining 9 (31%) patients detailed diagnostics was not performed, due to the patients' poor general condition. In 55% (11/20) of patients subject to detailed diagnostics, the primary neoplastic lesion was determined.Considering the study group, most patients with cancer of unknown primary origin were characterized by a favorable prognosis, which justified thorough diagnostics, in order to establish the primary neoplastic lesion. The introduction of diagnostic examinations enabled to identify the primary site of the tumor in more than 50% of patients. With the development of imaging methods one can expect improvement of unsatisfactory results, considering the detection of primary neoplastic foci.