Heterotopic tissue in lymph nodes. An unrecognized problem. Heterotopic tissue in lymph nodes is both unknown to clinicians and a potential source of confusion with metastatic disease. We reviewed the English literature and found 289 cases of heterotopic tissue in lymph nodes. The majority (84%) of these patients were operated on for malignant neoplasms. The most frequent sites of occurrence was the pelvis (67%), followed by the axilla (14%), neck (14%), groin (3%), abdomen (2%), and mediastinum (less than 1%). The tissue seen is site-specific and frequently resembles a neighboring organ. Three cases have been reported in which heterotopic tissue was mistaken for metastatic disease. These cases illustrate the importance of being familiar with heterotopic tissue in lymph nodes and identifying it when it does occur, to avoid inappropriate therapy. 