Sedation is frequently essential for successful MR imaging, and chloral hydrate is the most commonly used drug for this purpose in infants and children. Our experience with these patients suggested that this sedative is less effective in older children, even when administered in high doses. However, no prospective study comparing the efficacy of chloral hydrate sedation for children of different ages undergoing MR imaging has been reported. Accordingly, we performed a study to evaluate the effectiveness and safety of chloral hydrate sedation in children of various ages.The study included 300 infants and children, 1 month to 11 years old (mean, 3 years), who were given oral chloral hydrate, 100 mg/kg, for sedation before MR imaging. The maximum total dose administered was 2.5 g, which limited the study to children who weighed 25 kg or less. Sedation was considered successful when MR studies were completed and at least 95% of the images had little or no motion artifact.Sedation was successful in 273 (91%) o...