Background: Chronic pain from temporomandibular disorders remains an undertreated condition with debate regarding the most effective treatment modalities. Objective: The aim of the study was to investigate the treatment effect of an internet-based multimodal pain program on chronic temporomandibular disorder pain and evaluate the feasibility of a larger randomized controlled trial. Methods: An unblinded randomized controlled pilot trial was conducted with 43 participants (34 females, 9 males; median age 27, IQR 23-37 years) with chronic temporomandibular pain. Participants were recruited within the Public Dental Health Service and randomized to intervention (n=20) or active control (n=23). The intervention comprised a dentist-assisted internet-based multimodal pain program with 7 modules based on cognitive behavior therapy and self-management principles. The control group received conventional occlusal splint therapy. Primary outcomes included characteristic pain intensity, pain-related disability, and jaw functional limitation. Secondary outcomes were depression, anxiety, catastrophizing, and stress. Outcomes were self-assessed through questionnaires sent by mail at 3 and 6 months after treatment start. Feasibility evaluation included testing the study protocol and estimation of recruitment and attrition rates in the current research setting. Results: Only 49% of participants (21/43) provided data at the 6-month follow-up (internet-based multimodal pain program: n=7; control: n=14). Of the 20 participants randomized to the internet-based multimodal pain program, 14 started treatment and 8 completed all 7 modules of the program. Between-group analysis showed no significant difference for any outcome measure at 3- or 6-month follow-up-characteristic pain intensity (3 months: P=.58; 6 months: P=.41), pain-related disability (3 months: P=.51; 6 months: P=.12), jaw functional limitation (3 months: P=.45; 6 months: P=.90), degree of depression (3 months: P=.64; 6 months: P=.65), anxiety (3 months: P=.93; 6 months: P=.31), stress (3 months: P=.66; 6 months: P=.74), or catastrophizing (3 months: P=.86; 6 months: P=.85). Within-group analysis in the internet-based multimodal pain program group showed a significant reduction in jaw functional limitation score at the 6-month follow-up compared to baseline (Friedman: chi 2=10.2, P=.04; Wilcoxon: z=-2.3, P=.02). In the occlusal splint group, jaw function limitation was also reduced at the 6-month follow-up (Friedman: chi 2=20.0, P=.045; Wilcoxon: z=-2.3, P=.02), and there was a reduction in characteristic pain intensity at the 3- and 6-month follow-up (Friedman: chi 2=25.1, P=.01; Wilcoxon 3 months: z=-3.0, P=.003; Wilcoxon 6 months: z=-3.3, P=.001). Conclusions: This study was not able to demonstrate a difference in treatment outcome between an internet-based multimodal pain program and occlusal splint therapy in patients with chronic temporomandibular pain. However, the findings suggested that the internet-based multimodal pain program improves jaw function. The results also confirmed the treatment effect of occlusal splint therapy for chronic temporomandibular pain. Furthermore, because of the high attrition rate, this pilot study showed that a randomized controlled trial with this design is not feasible.