While much of the literature provides positive support for psychological interventions for chronic pain, two recent meta-analyses indicate small to moderate benefits only. This inconsistency in findings suggests that there are other treatment-related variables to consider. One possible consideration pertains to treatment format, as psychological models form the basis for both unidisciplinary psychology and integrated interdisciplinary treatments for chronic pain. Therefore, a comparative meta-analysis of unidisciplinary and interdisciplinary treatments was performed to determine whether there were differences in treatment effect size (ES) at post-treatment and follow-ups of up to one year. One specific treatment model, Acceptance and Commitment Therapy (ACT), was investigated as it was felt that this literature was extensive enough to perform the planned analysis, while also being circumscribed enough in size to make it feasible. In total, 29 articles met inclusion criteria, 13 reported outcomes for unidisciplinary ACT and 15 for interdisciplinary ACT. At both post-treatment and follow-up, interdisciplinary ACT had a greater ES for physical disability, psychosocial impact and depression compared to unidisciplinary ACT. No differences in ES were observed for pain intensity, pain-related anxiety, or pain acceptance. Findings remained the same when study heterogeneity was considered. There was a significant difference observed between treatment format and treatment duration – on average, unidisciplinary interventions were of shorter duration than interdisciplinary interventions. Moderation analyses examining the relation between total treatment duration and ES generally indicated a moderate positive relation between treatment length and ES. This relation was strong for psychosocial impact.