OBJECTIVE Although many studies have examined the reasons for repeated use of emergency medical service (EMS), little information is available concerning repeated ambulance use in Taiwan. This study evaluated the characteristics of repeated EMS ambulance use in an urban EMS system in Taiwan. METHODS Data from a local EMS computerized database for the period from January 1996 through December 1998 were collected for analysis. All calls to the dispatch center that resulted in EMS transports were included. Repeat users were identified by matching the user name, sex, age, and home address. Transports were categorized according to how many times the patient was transported by ambulance during the 3-year period: single use, one time; repeated use, two or three times; or frequent use, more than three times. RESULTS During the 36-month study period, there were 41,792 calls, with 13,076 non-transports (a non-transport rate of 31.3%). Of the 28,716 transports during the study period, 2,101 represented repeated or frequent use (7.3%); the rate of frequent use was 1.4% (406/28,716). The frequency of repeated use reached a daily first peak at 8:00 AM, with the second and third peaks at 1:00 PM and 7:00 PM. The mean age increased with increasing repeated use of transport (37.25 +/- 0.24 vs 41.55 +/- 1.03 vs 46.23 +/- 1.57 years, respectively; p < 0.001). The percentage of non-trauma missions increased with increasing repeated use of transport (26.3% vs 55.6% vs 73.2%; p < 0.001). Response time significantly increased for repeated use (analysis of variance [ANOVA], p < 0.001). The on-scene interval (time from arrival until departure) in the single-use group was shorter than in the repeated and frequent use groups (ANOVA, p < 0.005). CONCLUSIONS The results of this study indicate that the characteristics of repeat users of EMS transport differ from those of single users. Characteristics of service time, reason for transport, and interval to each subsequent call varied among different groups of users. Studies of repeat use under a wider range of conditions such as in rural EMS systems and after implementation of a priority-dispatch system are needed to determine the implications of repeated ambulance use.