The involvement of extra-abdominal/extra-pelvic sites by serous tumors after the diagnosis of an ovarian serous neoplasm of low malignant potential is extremely rare. In this study we present the clinicopathologic features of 12 such cases seen at our institution during a period of 19 years (1980-1999). The patients' age ranged from 19 to 50 years (mean 33 years). By FIGO staging the original ovarian tumors were distributed as follows: stage I, 4; stage II, 2; stage III, 5; unknown stage, 1. All patients were treated surgically. Ten patients also received adjuvant therapy (radiotherapy, 2; chemotherapy and radiotherapy, 4; chemotherapy, 3; intraperitoneal 32P, 1). The interval between the diagnosis of the ovarian neoplasm and the subsequent tumor involving an extra-abdominal/extra-pelvic site ranged from 4 to 240 months (mean 124 months). Sites of extra-abdominal/extra-pelvic involvement and the number of cases were as follows: left neck lymph nodes (LNs), 4; left and right neck LNs, 1; pleura, 2; lung, 1; mediastinum, 1; chest wall, 1; axillary and chest LNs, 1; and vertebral body, 1. Eight patients were treated with chemotherapy, 1 with radiotherapy, 2 with chemotherapy and radiotherapy, and 1 with surgery alone. Follow-up ranging from 5 months to 18 years was available in 11 patients. Six patients died of disease and 5 patients were alive with no evidence of disease. In this small series of cases, no definitive clinical or pathologic feature related to the occurrence of extra-abdominal/extra-pelvic serous tumors was found. Based on the LN involvement and the endosalpingiosis seen in some cases, these tumors might develop from circulating neoplastic serous cells or from areas of endosalpingiosis involving extra-abdominal/extra-pelvic sites.