Contrasting views in recent literature set the species number of the land snail Mastus in Crete (Greece) between 3 and over 17. In order to contribute to a better understanding of the spatial complexity of the genus, a biogeographical approach was employed in central and eastern Crete (6,000 km2) where distribution patterns of shell parameters of 1,600 samples totalling 5,500 specimens were analysed and evaluated at a 2 km scale. The results support grouping of the central and eastern Cretan populations in five obviously independent and genetically separated systematic entities, which are referred toas species. M. cretensis (Pfeiffer) and M. sitiensis Maassen are widely distributed in Crete. M. abundans Maassen, M. gittenbergeri Maassen and M. violacea Maassen occupy smaller ranges which largely conform with those of endemic species of the clausiliid Albinaria. The conclusions are only partly in agreement with the previous results of anatomical studies, but are consistent with predictions based on species-area relation data.