Costello syndrome is characterized by postnatal growth deficiency, mental retardation, curly hair, coarse characteristic face, and loose skin of hands and feet. Patients with this syndrome have a high incidence of cardiac involvement, including arrhythmia, atrial septal defect, and hypertrophic cardiomyopathy. We report a 16-year-old adolescent female with Costello syndrome who presents with hypercalciuria and urolithiasis.