Objective: The temporomandibular opening index (TOI) is endfeel distance divided by active and passive mouth opening. The asymmetry index (AI) is a measure of difference in left and right condylar heights. This study examined the relationship between AI and TOI in myogenous TMD and non-TMD patients. Method and Materials: Fourteen myogenous TMD patients diagnosed by the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) were recruited (1 man and 13 women) and 14 non-TMD patients (6 men and 8 women) were included as controls. Differences between the TMD patients and control group of non-TMD patients were determined by the two-tailed t test, while multiple linear regression analysis was used to examine the correlation between AI and TOI adjusting for sex and age. Results: AI and TOI were significantly higher (P = .001 and P = .045, respectively) among TMD patients. A significant positive correlation was found between TOI and AI for the TMD group (r = 0.84, P = .01) but not for the control group. Conclusion: A positive correlation was found between TOI and AI in the myogenous TMD group. Keywords: condylar asymmetry, myogenous, opening index, TMDs