Five cases of intrathoracic kidney are presented, and the literature is reviewed. The diagnosis was made incidentally in 3 patients who had chest radiographs because of upper respiratory tract infections and in 1 infant on a follow-up radiograph after recovery from hyaline membrane disease. The fifth patient had an abdominal mass. All 5 patients had a left intrathoracic kidney, and 2 had a left Bochdalek hernia. An intrathoracic kidney should be considered in the differential diagnosis of a posterior mediastinal mass.