The aim of this study is to determine the prognosis of patients with seizure onset from 1 to 24 months of age in respect to epilepsy, developmental outcome, and neurological status. It also aims to determine predictive factors regarding an unfavorable prognosis. Seventy-five patients were retrospectively analyzed. Univariate analysis revealed the following findings: (1) mental retardation at initial admission, abnormal neurological finding, infantile spasm, use of more than 1 antiepileptic drug, epileptic activity on electroencephalography (EEG) of neonatal seizure, and perinatal anoxia were significant risk factors with regard to developmental outcome; (2) mental retardation at initial admission, abnormal neurological finding, infantile spasm, use of more than 1 antiepileptic drug, epileptic activity on EEG, symptomatic etiology, history of neonatal seizure, and perinatal anoxia were significant risk factors regarding neurological status; and (3) mental retardation at initial admission, neurological abnormality, infantile spasm, use of more than 1 antiepileptic drug, epileptic activity on EEG, status epilepticus, symptomatic etiology, seizure frequency of more than once per week, history of perinatal anoxia, and neonatal seizure were significant risk factors regarding epilepsy prognosis. In addition, multivariate analysis revealed that neurological abnormality and use of more than 1 antiepileptic drug were significant for developmental outcome, that epileptic activity on EEG and use of more than 1 antiepileptic drug were significant for neurological status, and that perinatal anoxia, infantile spasm, and status epilepticus were significant for epilepsy prognosis. These findings suggest that neurological abnormality, use of more than 1 antiepileptic drug, infantile spasm, status epilepticus, and perinatal anoxia are unfavorable predictive risk factors regarding the prognosis of patients with seizures that have an onset from 1 to 24 months of age.