The carcinoma of unknown primary is a frequent clinical problem and represents a very heterogeneous group of neoplasms. Despite data in the literature indicating minimal success in determining the location of primary carcinomas, these patients continue to be evaluated exhaustively. Clinical treatment is guide by the pathological evaluation of the lesion and is very important the special pathologic techniques characterizing a potentially curable malignancy or patients for whom there is are a specific treatment. The majority of the patients are not included in these groups and they should be received treatment in clinical trials.