Vitamin D deficiency is common in intensive care unit (ICU) patients (50 - 82%) and is associated with multi-organ dysfunction. Vitamin D deficiency alters pathways of glutamine metabolism in critical illness, but the impact of vitamin D status on glutamine levels is poorly characterised. To assess the prevalence of vitamin D deficiency and its association with organ dysfunction and glutamine levels in a South African (SA) ICU. Records of 103 adult patients admitted to the Wits Donald Gordon Medical Centre ICU, Johannesburg, SA were retrospectively reviewed. 25-hydroxyvitamin D (25(OH)D) and glutamine levels were measured on admission. The association between admission vitamin D levels and glutamine levels, illness severity scores, organ support and outcomes was examined. On ICU admission, 66% (68/103) of patients were vitamin D deficient (<20 ng/mL) (95% confidence interval (CI) 56 - 75). Vitamin D deficiency was significantly associated with mechanical ventilation (40% v. 14%) (p=0.013) and a higher median sequential organ failure assessment (SOFA) score on admission (6 (interquartile range (IQR) 3 - 8) v. 4 (IQR 2 - 6)) (p=0.047) and on day 7 (5 (IQR 2 - 10) v. 2 (IQR 1 - 4)) (p=0.017). Median admission serum glutamine levels were 481 μmol/L, with 38% deficient (<420 μmol/L) (95% CI 28 - 48). Vitamin D deficiency status on admission was not significantly associated with median admission glutamine levels (p=0.66). Vitamin D deficiency is common in ICU patients in SA. Deficient patients were more severely ill and required more respiratory support. No significant relationship between deficiency and median glutamine levels was noted.