Breastfeeding has been recommended for the dietary treatment of infants with phenylketonuria, but studies documenting clinical experience in other inborn errors of metabolism are very few. Seven infants diagnosed with methylmalonyl-CoA mutase deficiency (n=2), ornithine carbamoyltransferase deficiency (n=1), propionic acidaemia (n=1), isovaleric acidaemia (n=1), maple syrup urine disease (n=1) and glutaric acidemia type I (n=1) were tried with breastfeeding over two years. After the control of acute metabolic problems, an initial feeding period with a measured volume of expressed breast milk plus a special essential amino acid mixture was continued with breastfeeding on demand and with the addition of a special essential amino acid mixture. Two patients with methylmalonic acidaemia and one patient with glutaric acidaemia type I tolerated breastfeeding on demand very well, with good growth and metabolic control for periods of 18, 8 and 5 months, respectively. In the patient with propionic acidaemia, on-demand breastfeeding continued for 3 months but was terminated after two acute metabolic episodes. The patient with isovaleric acidaemia had insufficiency of breast milk and formula supplementation ended with breast milk cessation. In the patient with severe ornithine carbamoyltransferase deficiency, breastfeeding was stopped owing to poor metabolic control. The patient with maple syrup urine disease also experienced problems, both in metabolic control and in insufficiency of breast milk, resulting in termination of breastfeeding. Breastfeeding of infants with inborn errors of protein catabolism is feasible, but it needs close monitoring with attention to such clinical parameters as growth, development and biochemistry, including amino acids, organic acids and ammonia.