The purpose of this study was to evaluate the patterns of recurrence in patients treated with Photofrin-mediated intraperitoneal photodynamic therapy (IP PDT). Sixty-six patients with gastrointestinal cancers, ovarian cancers, and sarcomas have been enrolled to date and 51 patients underwent IP PDT. Photofrin, 2.5 mg/kg, was administered intravenously 48 h prior to surgical debulking and intraoperative light treatment. Forty-five, and 49 patients were evaluable for response rates, and patterns of recurrence, respectively. Response to treatment was evaluated by CT or MRI scans of the abdomen and pelvis every 3 months. Patterns of recurrence were determined by evaluating the abdomen as a combination of different treatment regions. Of the 51 patients enrolled and treated with IP PDT two are alive without evidence of recurrence. Eleven of 45 patients showed no evidence of recurrence 3 months after treatment. No evidence of recurrence was noted in 7/17 sarcoma patients, 2 of 13 ovarian cancer patients, and 2 of 15 gastrointestinal cancer patients. The most common site of recurrence as determined by radiographs was the pelvis, which was noted in 19 of 49 (39%) patients. The presence of gross residual disease before light treatment (as determined by the attending surgeon) did not affect the site of recurrence. When studying those patients who had only locoregional recurrence, 9 of 33 evaluated radiographically and 10 of 24 evaluated operatively recurred only in peritoneal areas not previously involved with gross disease. The pelvis was the site with the highest rate of recurrence after IP PDT. A significant minority of patients recurred only in sites not previously involved with gross disease. Patients with gross residual disease before light therapy had similar recurrence rates to those without gross residual disease. Since sites involved with gross residual tumor often received boost doses of light, this could suggest a dose-response relationship for IP PDT.