BMC Public Health 2009, 9:251 http://www.biomedcentral.com/1471-2458/9/251 Discussion: If we show that our group training is (cost-)effective, more patients could be served, their quality of life could be improved while costs might be reduced. As the training is investigated in a heterogeneous patient group in the daily practice of a mental healthcare institution, its transfer to practice should be relatively easy. Trial registration: Nederlands Trial Register, NTR1609 Background The estimated prevalence of unexplained physical symp- toms in primary care ranges from 18 to 74% [1,2]. This huge difference in estimating prevalence is caused by mul- tiple definitions of unexplained physical symptoms such as Unexplained Physical Symptoms (UPS), Medical Unex- plained Physical Symptoms (MUPS), functional somatic syndromes and abridged somatization. We use the Diag- nostic and Statistical Manual of Mental Disorders IV -Text Revision (DSM-IV-TR) [3] and define unexplained physi- cal symptoms with the classification of 'undifferentiated somatoform disorder' and 'chronic pain disorder'. In the Netherlands, the estimated prevalence of unexplained physical symptoms in primary care is 18% [2]. Most of these unexplained physical symptoms can be classified as a somatoform disorder, of which 13.0% meets the criteria of undifferentiated somatoform disorder and 1.6% meets the criteria of chronic pain disorder [4]. In general, the DSM-IV-TR classifies symptoms without making assump- tions about etiology. However, the DSM-IV-TR does pre- sume psychological causes in the beginning, severity, increase or continuation of pain in chronic pain disorder. Therefore, we prefer to use the mere descriptive term 'Unexplained Physical Symptoms (UPS)', which corre- sponds with the DSM-IV-TR terms 'undifferentiated somatoform disorder' and 'chronic pain disorder' with the exception of the assumptions about etiology. Patients with UPS have high levels of psychosocial distress and healthcare utilization [5], for which cognitive behav- ioral therapy is shown to be most effective [6-9]. However, it is widely believed, that patients with unexplained phys- ical symptoms reject this kind of therapy. The conse- quences model is a positive exception. The key difference of this model compared to other cognitive behavioral models is its labeling of psychosocial distress in terms of consequences rather than as causes of UPS. Herewith, the consequences model fits both professionals' and patients' point of view. Refraining from labeling psychosocial dis- tress as causes of UPS corresponds with the lack of consen- sus among professionals about the causes of UPS, which is reflected in the ongoing debate about the position of somatoform disorders on Axis I or III in the next edition of Diagnostic and Statistical Manual of Mental Disorders [10,11]. Moreover, labeling psychosocial distress as con- sequences, matches the patients' perspective of UPS. This is reflected in the fact, that 81% of the patients in aca- demic medical care accepts an individual therapy based on the consequences model [12] and this individual ther- apy has positive outcomes in secondary care [13]. Unfor- tunately, in primary care, this high acceptance rate could not be reproduced and resulted in poor outcome [2,14]. We assume that the consequences model can maintain its positive outcome for patients in primary care, when we make some modifications. Firstly, we tailor this model more accurately to patients' perspective of their physical symptoms. Moreover, we put additional attention to relieve patients from being blamed for their symptoms. Furthermore, we make the group training easy accessible. Our aim is to investigate the (cost-)effectiveness of this easily accessible group training for patients in primary care conducted in the daily practice of our mental health- care institution, Riagg Rijnmond, The Netherlands. This study protocol provides a detailed description of the cog- nitive behavioral group training and the design of the ran- domized controlled trial investigating the (cost- )effectiveness of this training. Objectives The primary aim of this study is to investigate (cost-)effec- tiveness of our easily accessible protocollized group train- ing for patients with UPS in primary care conducted in the daily practice of a mental healthcare institution. The sec- ondary aim is to identify (personality-)variables enabling to predict this (cost-)effectiveness. Methods and design Design The (cost-)effectiveness of the group training is evaluated in a randomized controlled trial (see Figure 1). The study started February 2005. The inclusion of patients has ended in September 2008. The one-year follow-up period of the randomized patients will be finished in April 2010. Study population Patients are included when: 1. they are between 18 and 65 years old; 2. they are able to speak, read and write Dutch; Page 2 of 9 (page number not for citation purposes)