PURPOSE: To evaluate the sedative effect of add-on chlorpheniramine in children with neurologic diseases failed to sedate with chloral hydrate and midazolam. METHODS: Thirty three patients who had not been successfully sedated with oral chloral hydrate and intravenous midazolam for diagnostic examinations were attempted for sedation with intravenous chlorpheniramine at Chonnam National University Hospital from September 2007 to September 2012. The sedative effects were compared on the aspects of age, sex, body weight, dosage of drug and underlying neurologic conditions with the retrospective review of medical records. RESULTS: Among 33 patients, 26(78.7%) were successfully sedated and 7(24.2%) failed to sedate. The success rates were different by age and were decreased with age: 100%(0-4y), 84.6%(5-9y), 50%(10-14y). The effectiveness of chlorpheniramine was not significantly different in terms of ages, sex, body weight, dosage of drug and the underlying neurologic conditions-developmental delay, seizures or organic brain lesions. Children with ADHD(attention-deficit hyperactivity disorder), however, showed a significantly lower success rate than the non-ADHD patient group (28.5%, P=0.002). No serious side effects were reported except for one case with transient perioral cyanosis. CONCLUSION: Chlorpheniramine appeared highly effective in children with neurologic diseases who had not been sedated with chloral hydrate and midazolam. The efficacy seemed to be higher in the younger age groups and lower in children with ADHD.