We will evaluate 60 SCD subjects aged 7-21 years (30 with chronic pain and 30 without chronic pain) for VDD and to determine specific baseline characteristics including 25(OH)D levels, bone turnover rates measured by C telopeptide serum levels (CTx), opioid analgesic use, neuromuscular strength, evidence of skeletal complications on chest radiograph, depression and quality of life, serum levels of inflammatory cytokines and oxidative status and characteristics of the vitamin D receptor (VDR). These characteristics will be compared between those with chronic pain and those without chronic pain. We will have a 30 day run in observation period during which baseline pain status will be determined by daily pain diary report. All subjects with then be randomly assigned to receive vitamin D replacement therapy or placebo for six weeks and prospectively followed for six months. All subjects will be given daily recommended daily allowance (RDA) of calcium and vitamin D in the form of a soft chew containing 500 mg calcium and 200 IU vitamin D throughout the study period. The primary endpoints are changes in serum 25(OH)D and CTx levels and opioid analgesic use (mg/kg morphine equivalent). Secondary endpoints include changes in pain status as documented by diary, depression scores, quality of life scores, neuromuscular strength and changes in serum cytokine levels and markers of oxidative stress.