Lymphoma was found in 40 of 72 children with a mediastinal mass who had had an intrathoracic or extrathoracic biopsy or excision of the tumor performed at the Yale-New Haven (Conn) Medical Center between 1964 and 1977. The lymphomas were typically located in the anterior or middle compartment in children 2 years of age or older, and they were usually accompanied by fever, nocturnal sweating, weight loss, or pruritus. Thirty (75%) of the children with lymphoma had enlarged supraclavicular or cervical lymph nodes available for biopsy, whereas the other ten without palpable lymphadenopathy required a limited anterior thoractomy to obtain tissue for diagnosis. Careful preoperative selection makes extensive thoracotomy or attempts at excision of mediastinal lymphoma unnecessary. The findings in this retrospective study also emphasize the prevalence of lymphoma among mediastinal tumors seen in children older than 2 years of age.