Background Interdisciplinary multimodal pain therapy (IMPT) is mostly run in a group setting to encourage the exchange of experiences between patients and thus facilitate the change of pain-related attitudes and behavior. As is known from psychotherapy research, the fellow patients in a therapy group have a relevant influence on the success of the therapy for the individual patient.Objective We examined the extent to which therapy success in an IMST group is influenced by individual co-patient characteristics, such as cognitive behavioral pain management, the difference to their own pain management and the proportion of co-patients who repeat therapy.Method In a retrospectively planned investigation of the psychometric tests of all patients in an inpatient IMST between January 2013 and February 2020, the influence of fellow patient characteristics on clinically relevant changes with respect to various parameters of the severity of chronic pain disorders was analyzed using binary logistic regression analyses.Results We examined 636 treatment cases of which 540 were first-time stays. On each day of treatment, 5 fellow patients were present, 15% of whom had repeated the therapy. We were able to show that the proportion of fellow patients who repeat the therapy (p < 0.001; odds ratio, OR = 1.032) and the cognitive behavioral pain management of the fellow patients (p < 0.001; OR = 2.885) significantly increase the probability of achieving success in at least one of the parameters examined. An influence of a specific parameter on the success of therapy could not be proven.Conclusion Despite methodological limitations our results suggest that in patient groups of an IMST, patients with therapy experience and those with advanced cognitive behavioral methods for pain management should be combined with novices and patients who are still at the beginning of coping with the chronic pain disorder.