Despite Acute Insomnia being classified as a distinct nosological entity since 1979/1980 (ASDC/DSM III-R), there are no published estimates of its prevalence and incidence or data regarding transition to chronic insomnia or remission. This lack of data prevents an understanding of: a) the pathogenesis of insomnia and b) when and how treatment should be initiated. The aim of the present study was to provide such data from two community samples. Samples were recruited in the USA (n = 2861) and the North East of the UK (n = 1095). Additionally, 412 Normal Sleepers from the UK sample were surveyed longitudinally to determine prospectively incidence, transition, and remission rates for acute insomnia and assess whether the acute insomnia was a first episode, recurrent episode, or co-morbid with symptoms of other illnesses. The prevalence of acute insomnia was 9.5% (USA) and 7.9%(UK). The prevalence of three acute insomnia subtypes in the UK were; First-Onset Acute Insomnia 2.6%; Recurrent Acute Insomnia 3.8%; and 1.4% Co-morbid Acute Insomnia. The annual incidence of acute insomnia in the UK sample was between 31.2% and 36.6%. Remission rates fluctuated depending upon the definition of acute insomnia and whether the current episode was first-onset or recurrent. These findings provide preliminary insights into the natural history of insomnia. Such data will serve to inform how and when acute insomnia should be managed and whether such interventions may serve to diminish subsequent morbidity, particularly with respect to Major Depression. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.