The patient was identified via family screening at the age of 3 years when very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency was diagnosed in his sister by newborn screening. Enzyme and molecular analyses confirmed VLCAD-deficiency (VLCADD). Until the age of 8 years no severe illnesses occurred and the patient was completely asymptomatic without a fat-reduced and fat-modified diet. On regular follow-up, creatine kinase (CK) and liver transaminases were always in the normal range. A long-chain fat load with 1.5 g/kg body weight did not result in clinical symptoms, nor in elevation of CK or liver transaminases. At the age of 8 years, the patient for the first time complained of recurrent muscle pain after exercise. CK concentrations were elevated up to 20,000 U/L during one of these episodes. Medium-chain fat was supplemented. With a medium-chain fat-rich meal directly before exercise, muscle pain after exercise clearly decreased. In asymptomatic mild VLCADD, a fat-reduced diet may not be necessary, whereas in later infancy and adolescence, strenuous physical exercise may require additional energy from medium-chain fat.