The rejection of the old hypothesis concerning the role of occlusal factors in craniomandibular disorders has been suggested because of the lack of evidence supporting the hypothesis. However, it would be more helpful to seek tests that clearly show that the hypothesis is wrong. Most of the studies used to favor rejection of this hypothesis have incorporated designs precluding any causal conclusions on the role of occlusal factors. Time and resources have been wasted in repeated efforts to obtain what is only associative proof; studies designed to address the causal question are few. There are, as yet, no results clearly warranting the rejection of the hypothesis that occlusal factors are part of a causal complex of craniomandibular disorders.