OBJECTIVES The aim of this study was to assess the walkout rate and to identify influencing patient and visit characteristics on walkout. Furthermore, we assessed the reasons for leaving and medical care needs after leaving. METHODS In a 4-month population-based cohort study, the characteristics and influencing factors of walkout from two emergency departments in the Netherlands were studied. Afterwards, a follow-up telephone interview was conducted to assess the reasons for leaving and medical care needed. RESULTS A total of 169 out of 23 780 (0.7%) registered patients left without treatment, of whom 62% left after triage. Of the triaged walkouts, 26% had urgent or highly urgent medical complaints and target times to treatment had elapsed for 54% of the triaged walkouts. Independent predictors of leaving without treatment included being self-referred, arriving during the evening or night or during crowded conditions, and relatively lower urgency triage allocation. Ninety (53%) walkouts were contacted afterwards by phone. Long waiting time (61%) was the most-cited prime reason for leaving. Medical problems had resolved spontaneously in 19 of the 90 (21%) walkouts, and 47 (52%) walkouts reported having sought medical care elsewhere. For 24 of the 90 (27%) walkouts with persisting complaints, medical care was advised during the follow-up telephone call. CONCLUSION The average observed daily walkout rate was 1.4 patients over the 4-month period. In general, walkouts are self-referrals with lower urgent complaints, arriving during the evening or night shift or during crowded conditions. Most walkouts leave because of perceived long waiting times.