Vitamin D deficiency (VDD) is very common among African American adolescents and adults in the US, ten times higher than is seen in Caucasians. VDD is also quite common in sickle cell disease (SCD). Both VDD and SCD can cause chronic pain, compression fractures, and muscle weakness. The investigators believe VDD may contribute to poor musculoskeletal health and chronic pain seen in pediatric SCD. In this study, the investigators aim to show that children and adolescents with SCD and chronic pain have lower levels of vitamin D compared to those without chronic pain. The investigators also aim to determine the clinical characteristics in SCD patients related to their vitamin D status.