3-Methylglutaconic aciduria is a rare hereditary metabolic disorder characterized by increased urinary excretion of 3-methylglutaconic and 3-methylglutaric acids. Four clinical forms are recognized. This study presents the case of a 5-year-old male with type IV 3-methylglutaconic aciduria, initially diagnosed as “static encephalopathy.” The slow evolution and other clinical characteristics, together with cerebral magnetic resonance imaging (MRI) findings, eventually directed the diagnosis to organic aciduria that was confirmed by urine test. This study proposes that the clinical criteria for childhood cerebral palsy should be rigorously respected; neuroimaging studies, particularly MRI, should be conducted to confirm the diagnosis, especially in atypical cases.