The objectives of this study were to determine reasons for leaving a pediatric emergency department before physician evaluation, any adverse outcomes of those leaving, and to assess whether the presence of an ombudsman altered the pattern. This was a prospective follow-up study of all patients who left the pediatric emergency department of the Children's Hospital of Michigan before physician evaluation between October 24, 1991 and January 30, 1992. Information was obtained from medical records and a telephone questionnaire with the parent or guardian one week later. A control group of patients (n = 150) evaluated in the same period were randomly selected for comparison and matched for triage acuity score, shift, and weekday/weekend visit. Five hundred and twelve patients left during this period. Contact was made with 82% (419). Forty-three percent of patients left only because of a long wait, and an additional 19% included a long wait as one of the reasons for leaving. There was a significantly longer waiting time for walk-outs compared with controls (188 +/- 76.4 vs 93.6 +/- 64.9 minutes, P < 0.0001). Of the 419 patients followed, 256 (61%) were seen by a physician within seven days, and seven (1.7%) were hospitalized. Three hundred one (72%) were reported to be well; 108 (26%) were better. No deaths occurred. Hospitalization rates were significantly lower for patients who left compared with patients who stayed over the same period of time (7/419 vs 1931/16,990, P < 0.0001). The presence of an ombudsman was associated with an increase in walk-outs.(ABSTRACT TRUNCATED AT 250 WORDS)