We present the positive outcome of a pregnancy in a woman with severe classic maple syrup urine disease (MSUD). Maintaining the maternal plasma levels of leucine between 200 and 300 μmol/L allowed normal development of the foetus. Tolerance of protein and leucine increased continuously from the 16th gestational week until delivery. The patient was able to increase protein and leucine intake from 5 g to nearly 30 g and 300–3,000 mg/day, respectively. Weekly measurement of branched-chain amino acid (BCAA) concentrations and the assessment of dietary intake were used to adjust protein intake. After 41 weeks of pregnancy, she gave birth to a healthy baby girl and was able to breastfeed her daughter for 6 months during which time, the protein and leucine intake were lower than during pregnancy, but higher than with her usual pre-pregnancy diet. The development of the girl is normal at the age of 3 years.