Although there are different definitions of posterior bite collapse, only the classical definition of Amsterdam provides a definite diagnosis and treatment plan. This situation entails a subtle loss of the occlusal vertical dimension with resultant flaring of the maxillary incisors. Other causes for flaring, such as derangements of form and functions of lips and tongue, bruxism, habits, as well as the presence of advanced periodontal disease or malocclusions, should be ruled out before the diagnosis of posterior bite collapse can be made. The complexity of differential diagnosis is illustrated with three case reports.