PURPOSE: Sedation is often needed to perform an imaging study or procedure on a child. Although chloral hydrate is the most commonly used drug for pediatric sedation, little data are available for its efficacy or adverse effects. This study was undertaken to evaluate the efficacy of chloral hydrate for sedation and define any problems for using this agent in children. METHODS: The medical records of 324 infants and children, who were admitted at Chonnam National University Hospital from January 2005 to December 2005 were retrospectively reviewed. Age, sex, body weight, underlying diagnosis, performed procedure, dose of chloral hydrate, initial response, delayed response and other additional agents for sedation were reviewed. If the desired level(3 on the Skeie scale) was not reached within 30 min after the administration of drugs, sedation was considered as potentially failed. RESULTS: The average age of the study group was 27 months. Among 324 patients, 107 (33.0%) failed for chloral hydrate sedation. 77(47.8%) of the neurologically impaired 161 patients and 30(18.4%) of the unimpaired 163 patients failed on sedation with chloral hydrate. Among neurologically impaired cases, who had either developmental delay or seizures or both of them, 56.8%(25/44), 50.0%(58/116) and 64.7%(22/34) in each category respectively failed on sedation with chloral hydrate. CONCLUSION: In neurologically impaired patients, sedation by chloral hydrate was so difficult and prone to have adverse effects that it is recommended to supplement another drug than to administer the same drug again. However, further studies on effective methods of sedation are needed.