Background and aims Among chronic pain patients who are referred to participation in a multimodal rehabilitation program (MMRP), pain catastrophizing and dysfunctional pain coping is common. In many cases it may have driven the patient to a range of unsuccessful searches for biomedical explanations and pain relief. Often these efforts have left patients feeling disappointed, hopeless and misunderstood. The MMRP process can be preceded by a multimodal investigation (MMI) where an important effort is to validate the patient to create a good alliance and begin a process of change towards acceptance of the pain. However, whether the MMI has such therapeutic effect is unclear. Using a repeated single case experimental design, the purpose of this study was to investigate the therapeutic effect of MMI by studying changes in patients' experience of validation, alliance, acceptance of pain, coping, catastrophizing, and depression before and during the MMI process. Methods Participants were six chronic pain patients with high levels of pain catastrophizing (>25 on the Pain Catastrophizing Scale) and risk for long term disability (>105 on the Örebro Musculoskeletal Pain Screening Questionnaire) who were subjected to MMI before planned MMRP. For each patient, weekly self-report measures of validation, alliance and acceptance of pain were obtained during a 5-10-weeks baseline, before the MMI started. Subsequently, these measures were also obtained during a 6-8 weeks MMI process in order to enable comparative analyses. Additionally, pain coping, depression and pain catastrophizing were measured using standardized questionnaires before and after the MMI. Results Irrespective of experiences of validation and alliance before MMI, all six patients felt validated and experienced a good alliance during MMI. Acceptance of pain improved only in one patient during MMI. None of the patients showed clinically relevant improvement in pain coping, depression or catastrophizing after the MMI. Conclusions The patients did not change their acceptance and pain coping strategies despite of good alliance and experience of validation during the MMI process. Even if the design of this study precludes generalization to chronic pain patients in general, the results suggest that MMI may not have a therapeutic effect.