A prominent site for recurrence of retroperitoneal and visceral sarcoma is the abdominal cavity. In an attempt to understand the causation of local and regional recurrence, 21 sarcoma patients who had previously undergone "complete" surgical removal of the primary tumor were prospectively studied. Data were obtained retrospectively from the first operation and prospectively from the reoperative procedure at the Washington Cancer Institute. At the primary and reoperative surgeries, 9 abdominopelvic regions and 21 sites were scored and then cataloged in a standardized fashion. Tumor locations and surgical resections were statistically analyzed in an attempt to establish patterns of recurrence within the abdomen and pelvis. There was a significant difference in sites of recurrence when sarcomas that involved the parietal structures were compared with those that involved small bowel. Peritoneal implants (nodular recurrences) were uniformly present in both groups. In contrast, resection site recurrences were very common with primary sarcomas invested by parietal peritoneum, while they were absent in those covered by visceral peritoneum. When primary surgeries were compared with reoperations, there was an increasing intraabdominal dissemination; the mean number of regions increased from 1.81 to 5.13. The change in distribution of sarcoma deposits at reoperation was greatest in right upper (because of liver surface) central and pelvic abdominopelvic regions and lowest in the left upper and epigastrium. The four anatomic sites that revealed a significant increase in involvement at the time of recurrence were the greater omentum, liver surface, large bowel, and the cul-de-sac of Douglas (all p < 0.002). Regions with tumor involvement or regions subjected to surgical trauma at the time of primary sarcoma resection were significantly more likely to show sarcoma deposits than to be sarcoma free at reoperation. These data taken together may suggest that sarcoma tumor emboli are frequently present in the abdomen at the time of resection of the primary cancer and that these tumor emboli are entrapped in fibrinous material at or immediately adjacent to sites of surgical trauma and along narrow margins of resection. Tumor cell entrapment of sarcoma emboli released into the peritoneal cavity prior to or at the time of sarcoma resection may help explain the distribution of nodular and fusiform recurrence of abdominopelvic sarcoma.