BACKGROUND: Most cases of acute caffeine poisoning are easily diagnosed at initial hospital visits. Nonetheless, accurate diagnosis is sometimes delayed in some patients with this condition. Therefore, our aim was to determine the prevalence of delayed diagnosis of acute caffeine poisoning in the emergency department (ED). METHODS: A single-center retrospective observational study was conducted. All consecutive patients with acute caffeine poisoning who were admitted to our hospital from January 2016 to March 2024 were included. The primary outcome was the proportion of patients who did not receive a correct diagnosis initially in the ED. RESULTS: A total of 30 patients were included. The median age was 23 years (IQR 19-27), 24 (80%) were women, and 18 (60%) had psychiatric disorders. The diagnosis of acute caffeine poisoning was delayed in three patients (10%, 95% CI 0%-21%), among whom the initial diagnoses were encephalitis ( CONCLUSION: The initial diagnosis is missed in 1 of every 10 patients with acute caffeine poisoning. The presence of seizure as the initial sign was associated with delayed diagnosis of acute caffeine poisoning.