Pseudomyxoma peritonei, which is the seeding of the peritoneum by mucin-secreting metastatic deposits and the filling of the peritoneal cavity by these secretions, is a malignancy that even after excision of the metastatic areas has a poor prognosis, since no effective therapy has yet been established. Herein, we report five cases of pseudomyxoma peritonei that responded to a combined postsurgical therapy consisting of CDDP, 5-FU and MMC. A 59-year-old women had a complete response who underwent an appendectomy, a right ovariectomy, and an omentectomy due to pseudomyxoma peritonei, and was postoperatively given a 50 mg intraperitoneal administration of CDDP. Further, a subcutaneous implant-type reservoir was positioned intraperitoneally for postoperative chemotherapy. At 14 days after surgery, therapy was begun which consisted of CDDP (70 mg/m2/day 1), 5-FU (350 mg/m2/day 1) and MMC (6 mg/m2/day 1) administered intraperitoneally, and 5-FU (350 mg/m2/day 1-3) that was continuously infused by an intravenous drip. She received 4 courses of postoperative chemotherapy. As a result of this therapy, the serum CEA values, which had elevated postoperatively, fell to within their respective normal ranges, and at 44 months postoperatively, this patient remains alive. Given the results above, intraperitoneal administrations of this combined CDDP, 5-FU, MMC therapy may be effective for patients with pseudomyxoma peritonei.