There is limited experience in treating advanced colorectal cancer diagnosed during pregnancy because it is a rare occurrence; however, the incidence of colorectal cancer complicating pregnancy is expected to increase in the future. The combination of cancer and pregnancy is complicated and causes many dilemmas and concerns for the physician and patient. A delay in treatment may compromise maternal survival; however, therapy for the cancer may be harmful to the fetus. We present a case of a 26-year-old woman pregnant with twins who was diagnosed with metastatic colon cancer and treated with 5-fluorouracil, leukovorin, and oxaliplatin (FOLFOX) from 13 weeks gestational age to birth. The patient gave birth to healthy twins without malformations at 33 weeks gestational age. At follow-up examination, the 2-year-old twins are developing normally. The patient herself died 1 year after the initial cancer diagnosis. This shows a case in which the administration of FOLFOX during the second and third trimester of pregnancy caused no fetal harm. These findings are similar to those of previous studies in which systemic chemotherapy administered during the second and third trimester was relatively safe. However, we know that chemotherapy should be avoided during the first trimester.