The likelihood of metastatic spread of an extrathoracic primary tumor to the thorax depends on a number of factors, most importantly, the site and nature of the primary tumor. Although the plain chest radiography remains the first-line screening procedure, understanding the pattern of spread of various tumors and the frequency with which such spread occurs enables one to develop a rational approach to the use of other imaging modalities, particularly computed tomography, in evaluation of patients with known extrathoracic primary tumors.