The temporomandibular opening index (TOI) is a more useful measure of mandibular movement than linear mouth opening, since it is independent of age, gender, ramus length, and gonial angle. It is also useful when categorizing temporomandibular disorder (TMD) patients into diagnostic groups. Two subgroups of myogenous patients have been identified, one with a high and one with a low temporomandibular opening index. This study examined initial symptom severity in these two subgroups. Thirty-three (33) patients with a myogenous temporomandibular disorder were recruited. Twenty-six (26) were female and seven male. Eleven were found to be in the high temporomandibular opening index group and the remaining 22 in the low group. Symptom severity scores were determined prior to the start of treatment. Pain, joint sounds, headache, and neck pain were all rated by patients on a four-point verbal response scale. These symptom scores were compared between the two subgroups using the Wilcoxon two sample test. There appeared to be a significant difference between the two groups (p=0.0025). TMD patients with high temporomandibular opening index appeared to have more severe signs and symptoms of TMD than patients with a low index.