OBJECTIVES. To determine the incidence of thyroid abnormality in pregnant women with hepatitis C virus (HCV) infection and evaluate pregnancy outcomes with respect to thyroid function status. DESIGN. Prospective cohort study. SETTING. Tertiary care hospital. POPULATION. Pregnant women with HCV infection. METHODS. Seventy-eight HCV positive women had radioimmunoassay thyroid function tests. All were followed until delivery. Pregnancy outcomes were compared in women with and without subclinical hypothyroidism. MAIN OUTCOME MEASURES. Maternal and perinatal outcomes. RESULTS. Of 78 anti-HCV antibody positive pregnant women, 13 (16.7%) had abnormal thyroid-stimulating hormone (TSH) (>5 mIU/L; hypothyroid group) and the remaining 65 (83.3%) had normal TSH values (euthyroid group). None had abnormal free T4 levels. None showed evidence of fetal distress in labor or fetal asphyxia. In the hypothyroid group, 23% compared to 6.2% in euthyroid group underwent cesarean section (p=0.07). The incidence of preterm delivery (7.7% vs. 24.6%; p=0.28), mean gestation at delivery (38.2+/-1.8 vs. 37.5+/-1.8 weeks, p=0.19), and birthweight (2,687+/-430 g vs. 2,846+/-379 g, p=0.18) was comparable. Neonatal nursery admissions were comparable. CONCLUSION. The presence of subclinical hypothyroidism in pregnant women with HCV infection does not adversely affect short-term pregnancy outcomes.