Mitral valve prolapse (MVP) is known to be associated with thoracic skeletal anomalies. To determine the incidence and risk factors for mitral valve prolapse in the adolescent population with severe idiopathic scoliosis (IS), a prospective follow-up study on 139 adolescent patients with IS from the Pediatric Orthopedic Service was undertaken. Data collected included age, sex, medical and family history, physical exam, electrocardiogram and echocardiogram, spinal x-rays, and pulmonary function tests. MVP was detected by echocardiogram in 13.6% (19/139) of patients with IS as compared with 3.2% in 154 age- and weight-matched controls (p < 0.006). All patients with MVP were asymptomatic and a systolic click or murmur was detected on the single preoperative exam only in 37% (7/19) of them. Patients with MVP and IS weighed less (45.1 +/- 2.0 vs 51.8 +/- 0.1 kg, p < 0.002) as compared with those IS patients without MVP. The electrocardiogram was abnormal in 21% (4/19) of patients with MVP as compared with only 1.6% (2/120) of patients with IS but no MVP. The two groups did not differ with respect to age at diagnosis, severity of scoliosis, positive family history of scoliosis, or the presence of restrictive lung disease. Though IS was more prevalent in females (79%), the presence of MVP was not related to gender. MVP was persistent in 10 of the 19 patients reevaluated by echocardiogram 2-4 years after spinal surgery. We conclude that MVP is four times more common in patients with severe IS than in the normal adolescent population, and is associated with a lower body weight in IS patients with MVP than in IS patients without MVP. The persistent nature of MVP, even after corrective spinal surgery, may be related to factors other than geometric changes of the heart caused by abnormal thoracic curvature.