Chlormezanone is a widely prescribed muscle relaxant (1-3) whose pharmacology is well known (4-6), but the clinical effect of overdose still remains relatively obscure (1, 7, 8). We here report a recent case of a patient who had severe liver function impairment and other associated findings typical of chlormezanone overdose. The ingested dose (at least 12 g) is much larger than those of previous record (1, 2, 7, 8); thus, her critical presentation deserves to be reviewed.