A 29-year-old male presented with acute onset of weakness of all four limbs, preceded by severe physical exertion. Upon examination, he was found to have proximal weakness of all four limbs (lower limbs >> upper limbs) and fully dependent for his ADL. Investigations showed elevated CPK levels. A provisional diagnosis of inflammatory myositis was made, and he was treated with IV methylprednisolone for 5 days, followed by a tapering dose of oral steroids. His upper and lower limb weakness improved and he was able to do ADL independently, but minimal proximal weakness persisted in both upper and lowerlimbs. On follow-up, he continued to have proximal weakness of the lower limbs. Hence, muscle biopsy was done which showed Few hypertrophic and atrophic fibres with Perifascicular atrophy and there was no granuloma or vasculitis suggestive of non-inflammatory myopathy. Electron microscopic picture of muscle biopsy showed Abundant mitochondria with few markedly enlarged forms (giant mitochondria) and shows many swollen cristae. Vessels were unremarkable, Endothelial tubuloreticular inclusions were not seen suggestive of mitochondrial myopathy He was advised genetic analysis, but he denied consent for genetic analysis. The patient is under close follow-up.This case is a rare presentation of mitochondrial myopathy as acute onset weakness.