Interferon alfa-2a is a cytokine produced by recombinant DNA techniques and has antiproliferative, antiviral and immunomodulating effects. A number of case reports in the past have suggested relative safety of alpha-interferons during pregnancy with little or no effect on the fetus. A 15-year-old adolescent became pregnant while receiving alpha-interferon for essential thrombocythemia. She delivered a small-for-gestational age baby girl at 33 weeks gestation. The infant displayed a facial rash characteristic of neonatal lupus and transient thrombocytopenia; maternal and neonatal serologies were typical for drug-induced lupus. These findings suggest probable association between maternal use of alpha interferon and adverse effects in the fetus.