Vitamin D deficiency is common in sickle cell anaemia (SCA, HbSS), although its significance and optimal means of correction are unknown. We conducted an audit to assess the clinical significance of 25-hydroxy vitamin D (25-OHD) deficiency in children with SCA and to evaluate two methods of vitamin D supplementation. We audited 25-OHD levels in 81 children with SCA and looked for statistical associations with biochemical, haematological and clinical parameters. In a separate group of regularly transfused children with SCA, we compared changes in 25-OHD blood concentrations following treatment with either high-dose intramuscular ergocalciferol (n = 15) or 4 days of high-dose oral cholecalciferol (n = 64). Ninety-one percent of children with SCA had 25-OHD levels <20 μg/L. The 25-OHD levels were negatively correlated with increasing age (P < 0.001) but showed no significant relationship to laboratory measurements, transcranial Doppler velocities or hospital attendance. Both intramuscular ergocalciferol and oral cholecalciferol supplementations resulted in increases of 25-OHD blood concentration to normal levels. The mean dose of ergocalciferol was greater than that of cholecalciferol (7,729 versus 5,234 international units (IU)/kg, P < 0.001), but the increment in 25-OHD levels was significantly greater in the oral cholecalciferol group (6.44 versus 2.82 (ng/L)/(IU/kg), P < 0.001). Both approaches resulted in vitamin D sufficiency for about 120 days. Increased 25-OHD concentration was significantly associated with increased serum calcium concentration. Vitamin D deficiency is very common in SCA and can be effectively corrected with high-dose intramuscular ergocalciferol or 4 days of high-dose oral cholecalciferol. Prospective, randomised studies are needed to assess the clinical value of vitamin D supplementation.