Background: To assess the efficacy of multimodal pain therapy for chronic pain patients it is necessary to use suitable outcome domains as well as reliable and valid measurement instruments. Using pain intensity as an example, however, it is shown that there are critical issues with respect to suitability for chronic pain patients and the quality (e.g. content validity, feasibility and interpretability) of commonly used measurement instruments. Method: A focus group concept was designed to discuss the construct of pain intensity and common measurement instruments with chronic pain patients who underwent multimodal pain therapy. The focus group concept was tested in two pilot groups (N = 10) where eight issues previously established in guidelines were discussed. Results: The results of the pilot studies affirmed that the construct of pain intensity as well as the measurement instruments must be critically considered when applied to chronic pain patients and the effectiveness of multimodal pain therapy. The concept of patient focus groups proved to be a suitable method for patient participation. Integrating patients should be considered not only in discussions of existing pain scales but also in developing new measurement instruments.