The risk to the fetus after maternal rubella during the first 12 weeks of pregnancy has been established: 81 to 90 per cent of the fetuses are infected, and about 85 per cent of congenitally infected infants are damaged. Little is known about the risk to the fetus when maternal rubella occurs just before conception. Developmental abnormalities have been reported after such infection, but no systematic study of the outcome of the pregnancies has been made. The present authors report a prospective study of 61 pregnancies in which confirmed maternal rubella occurred shortly before or shortly after conception.From 1978 to 1987, 44 cases of maternal rubella, in which the rash appeared from 5 weeks before to 6 weeks after the last menstrual period, were reported to the Institut in Stuttgart. From 1975 to 1987, 17 cases were reported to the Surveillance Centre in England. Mixed products of conception or individual fetal organs from 39 aborted pregnancies were tested for rubella virus. Cord sera from 22 pregnancies that continued to term were tested for rubella IgM antibody.No evidence of intrauterine infection was found in 38 pregnancies in which the maternal rash appeared before, or within 11 days after, the onset of the last menstrual period (Table 1). The shortest interval between the appearance of the rash and fetal infection occurred when the rash appeared 12 days after the last menstrual period. All 10 cases in which the rash appeared 3 to 6 weeks after the last menstrual period resulted in fetal infection.Of the four IgM-positive infants, two had clinical evidence of congenital rubella at birth. One had a heart defect and failed to thrive; the other had a heart defect, microphthalmia, and hepatosplenomegaly; both later showed bilateral deafness. The other two IgM-positive infants appeared normal at birth but were reported to have bilateral deafness with no other abnormality at 14 months and at 2 years of age. All 18 IgM-negative infants appeared to be normal at birth. Information on subsequent progress has been obtained for 17, in all of whom development has been normal up to a mean age of 2 years (range, 1/2–5 years).