AbstractMutations in SURF1, a gene involved in cytochrome‐c oxidase (COX) assembly, cause COX deficiency and Leigh Syndrome (LS). Typical presentation is in the first year of life, with failure to thrive, psychomotor regression, ataxia, signs of brainstem dysfunction, and peripheral neuropathy. Progression is rapid and patients usually die of respiratory failure before 2 years of age. LS is characterized by symmetrical bilateral lesions in the brainstem and basal ganglia, revealed premortem as signal hyperintensities in T2‐weighted MRI imaging. Here, we describe a 10‐year‐old boy with a novel mutation in SURF1 associated with an unusually mild clinical course. At 39 months, there were no MRI lesions, and a follow‐up MRI at 8 years of age showed only brainstem and cerebellar involvement without lesions in the basal ganglia or subthalamic nuclei. These data confirm that the spectrum of MRI findings in LS is variable and that SURF1 mutations should be considered in patients with encephalomyopathy and COX deficiency even when early MRI findings are negative. © 2004 Wiley‐Liss, Inc.