Mitochondrial disease encompasses inherited disorders affecting mitochondrial function. A severe and untreatable form of mitochondrial disease is Leigh syndrome (LS), causing psychomotor regression and metabolic crises. To accelerate drug discovery for LS, we screen a library of 5,632 repurposable compounds in neural cells from LS-patient-derived induced pluripotent stem cells (iPSCs). We identify phosphodiesterase type 5 (PDE5) inhibitors as leads and prioritize sildenafil for its clinical safe