Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is most commonly due to m.3243A＞G mutation (El-Hattab et al 2015). Most patients have stroke-like episodes (SLEs), characterized by neurologic deficits not conforming to cerebral vascular territories (El-Hattab 2015). Corticosteroids are used to treat SLEs (Finsterer 2009), but can cause avascular necrosis (AVN) (Weinstein 2012). A 22-year-old male visited our hospital with a 3 week history of left leg weakness and 1 day history of left pelvic pain. He was diagnosed with MELAS nine years prior based on clinical findings of seizures, focal weakness, lactic acidosis, multifocal cerebral edema, and decreased activity of respiratory chain complex I; symptoms included hypertrophic cardiomyopathy, diabetes mellitus, epilepsy, sensorineural hearing impairment, and retinopathy. Since diagnosis, the patient had eight SLEs and was on prednisolone, coenzyme-Q, L-carnitine, vitamin B, and L-arginine. For acute SLE management, we prescribed dexamethasone and mannitol. Hip x-ray and magnetic resonance imaging showed bilateral femoral head osteonecrosis, Ficat and Arlet stage III (Ficat 1985). The steroid was tapered off and the patient underwent decompressive operation. This is the first report of AVN caused by glucocorticoids in MELAS. Glucocorticoids are effective in the treatment of SLE (Rossi et al 2002), but induce osteocyte apoptosis and damage the femoral head (Weinstein 2012). Diagnosis is difficult because AVN presents with ipsilateral weakness, as does SLE. Misdiagnosis could lead to increased dose and duration of corticosteroid therapy, aggravating AVN. A precise evaluation of symptoms is critical to distinguish AVN and begin prompt glucocorticoid tapering in patients with MELAS.