Vitamin K is a fat-soluble vitamin essential for posttranslational gamma-carboxylation of many proteins such as coagulation factors (II, VII, IX, X), osteocalcin, and proteins C and S. Neonates are prone for vitamin K deficiency and routine prophylactic supplementation of 1 mg of intramuscular vitamin K is recommended to neonates at birth. Patients with cystic fibrosis, Shwachman-Diamond syndrome, and other causes of exocrine pancreatic insufficiency are prone for vitamin K deficiency and will require supplementation along with pancreatic enzyme replacement therapy. Similarly, patients with chronic cholestatic liver diseases can develop vitamin K deficiency and need close monitoring and supplementation.