The objective of this study was to examine the pattern of emergency department (ED) use by frequent ED users over time. This study was a retrospective study of adults with more than 10 visits to a university hospital ED from 8/90 through 7/91. ED visits of this cohort to all hospitals in the metropolitan area were followed for 3 years. Records were reviewed for the etiology of each patient's ED visits. This cohort was comprised of 76 patients making 1,119 (1.9%) of the total 59,051 ED visits. Thirty-five of the 76 (46%) were frequent ED users in only the initial year. Thirteen of the 76 (17%) made more than 10 visits in all 4 years. The remainder had sporadic episodes of ED use. Thirty-five (46%) were evaluated at three or more EDs in years in which they were frequent users. Forty-two (55%) had a medical problem for the cause of the majority of their ED visits. Fifty-eight percent of patients making more than 10 visits in more than 1 year had psychiatric or substance abuse problems. The pattern of ED use in this cohort changed over time and was influenced by substance abuse and psychiatric problems. These data suggest that most patients do not remain frequent ED users over time.