This chapter focuses on the recurrent stroke attacks using a case of a 44-year-old right-handed woman who developed impairment of cognitive function, aphasia and muscle weakness after three stroke attacks at the ages of 40, 42, and 43, respectively, as an example. The patient was diagnosed as having mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) due to stroke-like episodes and A-to-G transition at nucleotide position 3243 (A3243G). To confirm the diagnosis of MELAS, pathological gene mutation and histological or biochemical abnormality of mitochondria as well as clinical features represented by stroke-like episodes are fundamental. Although there are no radical therapeutic strategies focusing on MELAS, the therapeutic effects of L-arginine for stroke-like episodes have been demonstrated recently. L-arginine infusions in the acute phase of attacks have significantly improved symptoms, and oral administration in the remitting phase has significantly decreased the frequency and severity of stroke-like episodes.