Epileptic seizures during infancy have a wide variety of clinical presentations and the outcome differs according to the etiology. Among the benign and rare causes of infantile seizures, Vitamin B12 deficiency has been encountered. Common symptoms of Vitamin B12 deficiency in infants include megaloblastic anemia, feeding difficulties, developmental delay, microcephaly, failure to thrive, hypotonia, lethargy, irritability, involuntary movements, seizures and cerebral atrophy. Involuntary movements and seizures may rarely be the initial symptoms of Vitamin B12 deficiency. Involuntary movements have also been reported to appear after initiation of Vitamin B12 supplementation in isolated cases, whereas, no such information exits for seizures. In this paper, three infants with Vitamin B12 deficiency associated with motor and mental retardation are reported because of long-lasting focal/multifocal epileptic seizures following the initiation of intramuscular Vitamin B12 treatment. Antiepileptics were introduced in addition to Vitamin B12. Seizures disappeared within a few days or weeks; electroencephalographic findings were normalized in a few months. No relapses occurred during the follow-up period.