We conducted an observational study of 539 episodes of alcohol withdrawal in a general hospital, to determine the natural history, the incidences of seizures, hallucinations and delirium, and the risk factors for these events. The reaction began soon after arrival, at a median time of 5 h, and resolved at a median time of 22 h. Patients with a blood alcohol level of zero were in withdrawal on arrival, and only four patients had reactions lasting 120 h or longer. Complications were observed in 113 patients (21%) during the admission. Seizures occurred on arrival, hallucinations usually in the first 24 h and delirium in the first 48 h. No mortality was associated with alcohol withdrawal itself, but complications did extend length of stay by a median of 4 days, with delirium contributing most to the increase. Patients over 70 years of age or admitted with seizures had an increased risk of complication, but the greatest risk was associated with a delay in assessment of > 24 h. We conclude that in general hospitals, the alcohol withdrawal reaction becomes established very early, and detection and monitoring of patients within the first 24 h is the most important element in management.