Coffin-Lowry syndrome is a rare X-linked disorder characterized by craniofacial and skeletal abnormalities, mental retardation, short stature, and hypotonia. An 18-year-old man with morphologic features characteristic of Coffin-Lowry syndrome was referred to our institution for valve disease surgery for worsening cardiac failure. Echocardiography showed severe mitral valve regurgitation associated with tricuspid valve regurgitation. Mitral valve implantation with a biological valve and tricuspid annular plication with a ring was performed. The ascending aorta was hypoplastic. Both the mitral papillary muscle originating near the mitral annulus and the chordae were shortened. The patient's postoperative course was uneventful and his cardiac failure improved.