Glutaric aciduria type I is a congenital metabolic disease caused by an enzymatic defect in the degradation of the amino acids lysine and tryptophane. This article presents five Norwegian patients with this condition. Early clinical features may be similar to those of encephalitis. The further clinical course is dominated by choreoathetosis, hyperkinesis and spasticity. The diagnosis is made by tracing enhanced glutaric acid in the urine. The treatment is a low protein diet containing only small quantities of lysine and tryptophane. Four of our patients underwent a neuropsychological examination. Despite the fact that such patients are difficult to test, our examination indicates that the condition has a greater effect on motor than on cognitive functions.