We report a possible association of unilateral absence of a clavicle with rapidly progressive scoliosis. Cleidocranial dysplasia (CCD) is an autosomal dominant disorder that is characterized by defective bone formation. The clavicle, pelvis, and skull are the most commonly affected bones. A review of the literature found two cases of CCD and scoliosis. Unilateral absence of the clavicle in association with rapidly progressing scoliosis has not been previously reported. Review of the patient's charts and radiographs from age 8 to 17 years, 5 years after treatment with posterior spinal instrumentation is presented, together with a review of the literature. Our patient initially presented without any spinal deformity until age 9, when she had a 10 degree curve between C-8 and L-T. Eighteen months later, the curve progressed to 52 degrees, Risser 1. Associated anomalies include posterior-element hypoplasia of the thoracic spine and posterior fusion of C4-6. She was treated with posterior spinal instrumentation from C-8 to L-4 without complications. Correction was maintained at 5-year follow-up. There may be an association between unilateral absence of the clavicle and rapid progression of scoliosis in immature children. We hypothesize that the asymmetrical influence of the unilateral absent clavicle may have played a causative role in her rapidly progressive scoliosis.