352 British Journal of Hospital Medicine, June 2014, Vol 75, No 6 © 2 01 4 M A H ea lth ca re L td Introduction Vitamin B12 is a water-soluble vitamin which is found exclusively in food of animal origin such as meat, fish, eggs and milk (Quentin et al, 2012). It acts as an important coenzyme in the conversion of homocysteine to methionine (folatedependent reaction) and the conversion of L-methylmalonyl coenzyme A to succinyl-CoA (Quentin et al, 2012). Dietary vitamin B12 deficiency is relatively common in the elderly but is rare in children. It is almost exclusively seen in infants of breastfeeding mothers who eat a strict vegetarian diet (Agrawal and Nathani, 2009; Ide et al, 2011). Vitamin B12 deficiency in children can present with reversible megaloblastic anaemia, oedema (caused by hypoalbuminaemia), neurological manifestations such as irritability, apathy, developmental delay, ataxia, paraesthesia, hyporeflexia, hypotonia, tremor, seizures, loss of acquired motor abilities and coma (Reghu et al, 2005). An interesting observation seen in infants with vitamin B12 deficiency is difficulty in weaning on to solid foods (Reghu et al, 2005; Ide et al, 2011). This article describes a young child with vitamin B12 deficiency who presented with failure to wean on to solid foods and developmental delay.