We experienced four boys (two siblings) whose cardiac valves were all prolapsed, which have never been reported as a recognized disease. All had hyperextensive joints without any other stigmata of Marfan or Ehlers-Danlos syndrome. The severity and progression of regurgitation of each valve differed by a case, though they had similar echocardiographic findings consistent with the diagnosis of multiple floppy valves. Three of the four patients had severe aortic regurgitation, and two received aortic valve replacement. Their excised valves revealed myxomatous degeneration. The tricuspid valves were more thickened and redundant than the mitral valves. Although three patients had moderate tricuspid regurgitation, none of them had clinically important mitral regurgitation. We recommend aortic and/or mitral valve replacement, whenever the regurgitation exacerbates left ventricular dilatation. Aortic regurgitation deteriorated rapidly in one case due to valve rupture. In this case, moderate tricuspid regurgitation was relieved after aortic valve replacement. Skin fibroblast did not show any abnormalities in collagen biosynthesis.