Aims: To test the hypothesis that temporomandibular disorder (TMD) patients have characteristic diurnal patterns of pain that are associated with diurnal or nocturnal parafunctions. Methods: Experience sampling methods were used to obtain information on pain from subjects (n = 84) diagnosed, according to the Research Diagnostic Criteria for TMD, with myofascial pain, myofascial pain and arthralgia, disc displacement, and from non-TMD controls. Variations in pain as reported on the pager questionnaire form were modeled as linear, exponential, and quadratic effects. Results: Between 8.7% and 23.8% of TMD subjects with pain showed significant patterns to their daily pain reports, compared to 4.5% of non-TMD controls. Groups did not differ significantly in the proportions of those with increasing (59.5%) vs. decreasing (40.5%) pain levels. Self-reported clenching during the day and grinding at night were weakly associated with an increasing or decreasing pattern of pain during the day (P .10). Pain levels during weekends were significantly lower for all groups. Conclusions: Strongly linear or curvilinear patterns of pain were not characteristic of this sample of subjects. More than half the subjects reported slightly increasing pain during the day, but the variability within groups was considerable. Increasing and decreasing patterns of pain were independent of self-reported daytime and nighttime clenching and grinding. Self-reported pain patterns may not be used to reliably infer the times when parafunctional activities occur. The presence of lower pain levels during the weekend probably reflects reduction in psychosocial stressors associated with the work week. Keywords: diurnal variation, experience sampling, modeling, pain, temporomandibular disorders