Vitamin B₁₂ deficiency in children can rarely cause neurologic manifestations. In this series, 14 pediatric cases (median age 11 months) have been described in whom association of vitamin B₁₂ deficiency with developmental delay or regression was observed. Severe to profound delay was present in 8 (57%) patients. All the patients were exclusively or predominantly breast-fed and 10 of 12 mothers had low serum vitamin B₁₂ levels. Three to 6 months after treatment, a mean gain of development quotient of 38.8 points was seen in 7 follow-ups. In settings with a high prevalence of vitamin B₁₂ deficiency, this association should be actively searched for.