BACKGROUND.: Vitamin D is increasingly recognized for its roles in non-skeletal disorders. Patients with sickle cell disease (SCD) have a high prevalence of vitamin D deficiency but data are limited with respect to possible associations between low vitamin D and acute vaso-occlusive complications. We examined whether vitamin D deficiency is associated with acute pain and acute chest syndrome (ACS) in children with SCD. PROCEDURE.: A cross-sectional study was conducted in 95 children with SCD who had serum 25-hydroxyvitamin D (25-OHD) measured during comprehensive care examinations. History of acute pain and ACS within two years of obtaining 25-OHD was collected. Associations between 25-OHD levels and acute vaso-occlusive events were analyzed by logistic regression. Odds ratios and 95% confidence intervals were calculated for the risk of pain and ACS associated with vitamin D deficiency (25-OHD <20 ng/ml). RESULTS.: Subjects were 3–20 years old (median 10.6); 48 males, 47 females; 46 African, 49 Hispanic; 72 SS, 20 SC, 1 S/βThalassemia, and 2 S/βThalassemia. Median 25-OHD was 16 ng/ml. Fifty-six (59%) were vitamin D-deficient. Thirty-one (33%) and 29 (31%) had at least one episode of pain and ACS, respectively. Serum 25-OHD was significantly associated with pain (P = 0.0121) but not with ACS (P = 0.628). Of those with pain, 73% (23/31) were vitamin D-deficient while 26% (8/31) had 25-OHD ≥20 ng/ml (P = 0.04, OR = 2.7, 95%CI = 1.05–6.94). CONCLUSIONS.: Our findings emphasize the high prevalence of vitamin D deficiency and its potential association with acute pain in SCD. Correcting low vitamin D may offer a simple, low-cost intervention to help reduce acute vaso-occlusive complications. Pediatr Blood Cancer 2015;62:643–647. © 2015 Wiley Periodicals, Inc.