An increased prevalence of mitral-valve prolapse occurs in several connective tissue dysplasias, including Marfan syndrome, Ehlers-Danlos syndrome, and pseudoxanthoma elasticum. We evaluated 57 patients diagnosed as having the Stickler syndrome for mitral-valve prolapse by auscultation and two-dimensional echocardiography. The diagnosis was made on the basis of craniofacial and musculoskeletal abnormalities, sensorineural hearing loss, eye defects, and a family history of Stickler syndrome. Twenty-six patients (45.6%) had mitral-valve prolapse, including 11 of 22 females (50.0%) and 15 of 35 males (42.9%). The age range of our study population was 4 to 60 years. Prevalence of mitral-valve prolapse did not increase with age. Nine patients (34.6% of those with mitral-valve prolapse) had the click-murmur syndrome; only one of them was symptomatic. Because of the growing list of complications associated with mitral-valve prolapse, all patients with Stickler syndrome should be evaluated by auscultation, electrocardiogram, and echocardiography. Those with mitral-valve prolapse should be advised to have periodic follow-up and to instruct physicians caring for them of their need for antibiotic prophylaxis with certain surgical procedures.