The purpose of this study was to identify the proportion of adult patients at our institution who require sedation to tolerate MR imaging. We also wished to identify whether the type of study and patient age or sex was associated with a variation in the use of sedation. A total of 939 patients, 18 years of age or older, underwent MR imaging at a large university hospital during a randomly selected 7-week period. Age, sex, type of study, number of prior MRI's, and use of sedation were identified in this group. Patients requiring sedation were compared by these criteria to all non-sedated members over 18 years of age in the cohort who acted as a control. Of the 939 patients 134 (14.3%) required oral sedation, i.v. sedation, or general anesthesia to tolerate MRI. This group was 35.8% male, 64.1% female (control group 48.1% male, 51.9% female). Of those requiring sedation, 89 patients (66.4%) were having brain MRI (male n = 29 or 32.6%, female n = 60 or 67.4%). In the control group 461 patients (57.3%) were having brain MRI (male n = 209 or 45.3%, female n = 252 or 54.6%). The mean age of the sedated group was 60.75 (range 19-91). The non-sedated group had a mean age of 67.3 (range 28-93). The sedated group had undergone a mean of 1.56 prior MR studies (range 0-16); the control group had a mean of 0.9 prior studies (range 0-7). Sedation was more commonly utilized in women than men, in patients having brain MRI, and in patients who had undergone prior MRI procedures. The identification of a population having the greatest need for sedation may aid in the development and selection of methods of stress reduction which will result in greater patient comfort, reduction in motion artifact, and fewer prematurely terminated studies.