Transcobalamin deficiency (OMIM 275350) is a rare autosomal recessive disease presenting with nonspecific clinical features in early infancy. We report the clinical and laboratory manifestations of 7 children diagnosed with transcobalamin deficiency. All patients were admitted between 2 and 4 months of age with anemia, thrombocytopenia, and hyperhomocysteinemia. The most common complaints at admission were pallor, weakness, and poor feeding. Genetic analysis was performed in 5 patients and it revealed the same homozygous mutation. We initially treated all patients with intramuscular injections of a maximum of 1 mg cyanocobalamin (CN-Cbl) daily and with a final dose of 1 mg per week. Hemoglobin and platelet counts significantly decreased upon decrease or cessation of CN-Cbl therapy. The patients were reevaluated between 2 and 4 years of age and all had delay in speech and walking. In conclusion, 1 mg of intramuscular CN-Cbl every week suffices for hematological improvement but not for normal neurological development in patients who all had relapse due to decrease or cessation of treatment.