Acute confusional state (ACS) relates to a sudden alteration of the mental status. The impairment may be global or confined to a specific faculty of higher cortical function. Such specificity does not depend on the nature of the pathological process, but rather on the anatomical location of the area of the brain which is involved. In the absence of relevant medical history and associated signs and symptoms, the differential diagnosis of ACS may be difficult. Two case reports of unusual causes of ACS are presented: basilar migraine manifesting as transient global amnesia, and absence status. These are followed by a brief review of etiological causes of ACS commonly encountered in the pediatric practice, and a more detailed review of rare causes, such as non-convulsive epilepsy and migraine. A list of auxiliary tests for cases which are not readily diagnosed is presented.