Clinical features, magnetic resonance, and biochemical studies are reported in 7 children with pyruvate dehydrogenase (PDH) deficiency. These findings confirm the diverse clinical presentation of this condition, although neurological abnormalities are consistent features. Imaging results are also varied. Six of the children were investigated with proton magnetic resonance spectroscopy and lactate was demonstrated in brain in all patients. Regional variation in the lactate signal was observed in those patients in whom 2 regions were examined. Advances in molecular genetics have provided some explanations for the clinical variation in pyruvate dehydrogenase deficiency.