This double-blind study evaluated the short-term effect of iontophoretic delivery of dexamethasone on the signs and symptoms of temporomandibular disorders in patients who had concurrent temporomandibular joint disc displacement without reduction and capsulitis. Twenty-seven patients with this clinical diagnosis were randomized to one of three groups: treatment group (dexamethasone sodium phosphate and lidocaine hydrochloride); control group (lidocaine hydrochloride); and placebo group (pH-buffered saline). Pretreatment and posttreatment data included items to calculate Helkimo's Anamnestic Dysfunction index, Helkimo's Clinical Dysfunction index, the Symptom Severity Index, and the Craniomandibular Index (CMI). The CMI is composed of the Dysfunction index (DI) and Muscle index. Analysis of variance showed no baseline differences on these measures between the three groups. Pretreatment and posttreatment values were compared with the paired t tests. Posttreatment, the treatment group had an increased mean maximal active mandibular opening of 6 mm (P = .02), increased mean lateral excursion of 1.2 mm to the noninvolved side (P = .05), and reduced mean DI scores of 0.51 to 0.39 (P = .01); no statistically significant decrease in pain symptoms was reported. Analysis of variance showed a significant difference in the DI scores (P = .04) between groups from pretreatment to posttreatment, with the treatment group showing the greatest improvement in the DI scores relative to the other two groups. No other questionnaire items, exam items, or resultant indexes showed changes in any of the groups at P < or = .05. These results suggest that iontophoretic delivery of dexamethasone and lidocaine was effective in improving mandibular function, but not in reducing pain, in temporomandibular disorders patients who had concurrent temporomandibular joint capsulitis and disc displacement without reduction.