Occlusal and incisal tooth wear were evaluated for the purpose of assessing their prevalence, severity and distribution in a selected Swedish high-wear patient sample and in a young adult Saudi non-patient population. Furthermore, an attempt was made to investigate, by means of a questionnaire and a clinical examination, the association of various factors with wear; any observed associations were further analyzed with reference to possible cause and effect relationships. The scales used for evaluating the severity and the progression of wear provided high inter- and intra-observer concordances. The results revealed a high wear experience in the Saudi population compared to Western equivalents. Dietary, para-functional, anamnestic, occlusal and salivary factors exhibited certain correlations with wear. Progression of tooth wear was shown to be a slow process in the Swedish sample. The common element of a harsh desert terrain in the Saudi sample may constitute the dominant passive abrasive etiological factor in this population. While progression of wear seems to be of a "linear" nature in the Saudi population, it is postulated that wear in Western populations may, in addition to a "linear" deterioration, occur in "bursts", coinciding with the presence of certain causative factors. The results from this study also indicate that the effects of excessive function, including that of wear, on certain dentoalveolar morphological features are similar in modern man and his ancestors. On the basis of the findings, not only is the multifactorial etiology of occlusal tooth wear a reality, but so too is the complex interdependence of these factors in the prevalence, severity, distribution and progression of wear.