Varicella infection in the first trimester has been associated with a constellation of congenital abnormalities. The incidence of the congenital varicella syndrome is unknown, although it has been reported to be as high as 9%. In a prospective study performed between 1986-1990, 40 patients were identified who had first-trimester varicella infection. Pregnant patients were referred from physicians in the perinatal regional network after developing the classical picture of varicella infection. Targeted fetal ultrasound examinations were performed between 16-20 weeks' gestation in all cases and neonatal outcome was determined. Of the 40 patients, three had first-trimester losses and another underwent an elective termination of pregnancy after counseling. Of the remaining 36 women, one had fetal omphalocele. Thirty-five pregnancies continued until term, and no infant had features of the congenital varicella syndrome at birth. Other than the case of omphalocele, no major congenital anomalies were identified. This study, the largest series of patients with first-trimester varicella infection, showed an incidence of congenital varicella syndrome of 0% and an incidence of congenital anomalies of 3% (range 0-8% at 95% confidence level).