Aims-To study retrospectively the effects of treatment and the clinical outcome in 12 patients with glutaric aciduria type 1; and to compare the outcome in 6 patients diagnosed as a result of family screening with 6 patients who were diagnosed late after symptomatic presentation. Setting-The National Centre for Inherited Metabolic Disorders, The Children's Hospital, Dublin, ireland. Result-Four of the 6 children detected on screening are developmentally normal, 1 died, and the remaining 1 has mild mental handicap. All 6 of the late diagnosed symptomatic group suffered dyskinetic cerebral palsy and 5 have died. Conclusion-Experience of 50 patient treatment years has shown that early intensive management can alter the natural history of this rare disorder.