We report the two first prenatal diagnoses in an Italian family with a proband affected by neonatal carbamyl-phosphate synthetase I deficiency in which molecular analysis identified V457G and Q810R amino acid substitutions. We performed a prenatal diagnosis on genomic DNA isolated from chorionic villus and amniotic fluid samples collected at 13 weeks of gestation. In the first pregnancy, the fetus was compound heterozygous for the mutations and termination of pregnancy was elected. The genetic lesions were also confirmed on genomic DNA isolated from the fetus's liver and skin fibroblasts. A few months later, we performed a second prenatal diagnosis in this family. The second fetus was heterozygous for the wild-type alleles. The pregnancy was continued and a girl was born at 41 weeks of gestation. We have confirmed the wild-type state on the baby's DNA.