Diffusion-weighted magnetic resonance imaging (DW-MRI) of the brain was performed in two patients with methylmalonic aciduria who presented signs and symptoms of neurological involvement without metabolic decompensation. Patient 1 presented acute metabolic stroke and patient 2 presented subacute encephalopathy. Brain DW-MRI confirmed very recent damage in patient 1, while the absence of brain lesions on brain DW-MRI indicates the development of more chronic damage in patient 2. Brain DW-MRI represents an additional and complementary tool in the assessment of brain damage in methylmalonic aciduria patients who develop neurological syndrome.