Interferon-alpha (IF alpha) is used for the treatment of myeloproliferative diseases and chronic viral illnesses. Because the agent has antiproliferative activity, its effects on a fetus are a concern. We encountered a 40-year-old Japanese woman who inadvertently received IF alpha during pregnancy for the treatment of HCV hepatitis. The patient received 5 million units of IF alpha 2 to 4 times per week (total dose of 315 million units) between 13 and 33 weeks gestation. The patient delivered a normally formed healthy male infant, weighing 2,252 g at 37 weeks of gestation. The infant at 20-month-old exhibited normal growth and neurological development when last examined. Literatures were reviewed to determine the effects of IF alpha on the fetus. There have been 27 infants born to 26 mothers, including the present case, who were exposed to IF alpha in utero. Six women (23%) were administered IF alpha inadvertently during pregnancy. Four women (15%) gave birth prematurely. Although 6 infants (22%) were affected by intrauterine growth retardation (IUGR), there were no IF alpha-related malformed infants. These results suggested that an inadvertent administration of IF alpha during pregnancy may occur, but in that case IF alpha may not induce congenital malformations. These findings may encourage such women to continue pregnancy.