Mastoid hypocellularity is frequently used as an indicator of chronic otits media in paleopathological investigations. The condition can be caused by a poor development of air cells during infancy and early childhood (primary hypocellularity) or by obliteration of air cells with bone during later life (secondary hypocellularity). We performed a macroscopic, radiographic, and microscopic study of pneumatization patterns in 151 mastoid processes of individuals from an early-medieval cemetery in Germany, with emphasis on the architecture of the nonpneumatized portion of hypocellular mastoid processes. Two types of primary mastoid hypocellularity were distinguished. The first was characterized by a poorly defined boundary between the pneumatized portion and the nonpneumatized portion and a trabecular thickening in the spongy bone of the latter. The second showed a well-defined boundary between the pneumatized portion and the nonpneumatized portion and normal spongy bone architecture in the latter. The key feature for the diagnosis of secondary hypocellularity was the recognition of the walls of former air cells. Our observations closely match the histopathological findings by Wittmaack (Wittmaack: Über die normale und die pathologische Pneumatisation des Schläfenbeins. Jena: Gustav Fischer ), who developed a concept of the normal pneumatization process of the temporal bone and the pathogenesis of aberrant pneumatization. We agree with Wittmaack's view that two types of primary mastoid hypocellularity can be distinguished morphologically. Regarding the pathogenesis of these types, we, however, conclude that Wittmaack's concept needs to be revised and updated. Further studies are required to establish the relationship between morphological findings in cases of mastoid hypocellularity and the health status of individuals. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc.