Introduction: Multiple acyl‐coenzyme A dehydrogenase deficiency (MADD), also called glutaric aciduria type II, is an inherited metabolic disorder resulting from a deficiency in electron transfer flavoprotein (ETF) or of its ubiquinone oxidoreductase (ETF‐QO). It usually occurs in the neonatal period or in early infancy and, very rarely, in adolescents and young adult patients. Methods: We report the case of a 55‐year‐old woman who developed a painful subacute myopathy. Results: Lipid accumulation was found at biopsy. MADD was confirmed by plasma acylcarnitine profile and by assessment of ETF‐QO activity in muscle. Conclusions: This study demonstrates that metabolic myopathies usually found in infancy may be also diagnosed in older patients. MADD may be easily treated by riboflavin and coenzyme Q10 and therefore should be included in the differential diagnosis of adult‐onset painful myopathy. Muscle Nerve 43: 444–446, 2011