Colorectal cancer during pregnancy is very rare. We report two additional cases of rectal carcinoma. A 34-year-old woman with an obstructive adenocarcinoma of the rectal region was diagnosed at labor. A 35-year-old woman with an adenocarcinoma of the rectal region was diagnosed at 32 weeks of gestation and underwent a cesarean section and rectal resection at 35 weeks of gestation. A retrospective review of the Japanese literature was performed to identify patients who appeared to have primary colorectal cancer during pregnancy. Thirty-six patients with colon cancer (75.0%), 10 (20.8%) with rectal cancer, and two (4.2%) of unknown sites have been reported in Japanese series. The average age of the mother was 32.2 years. The calculated incidence of colorectal cancer among Japanese pregnant women was one case per 502,316 live births during the years between 1986 through 1995. Although the majority of colorectal cancers diagnosed during pregnancy are rectal carcinomas, the patients in Japan were predominantly complicated by colon cancer. The fetal risk seems small, because there were no cases of colorectal cancer metastatic to the products of conception.