The validity and clinical use of a recently developed instrument to assess health care needs of patients with a physical illness, called INTERMED, is investigated. The INTERMED combines data reflecting patients' biological, psychological, and social characteristics with information on health care utilization characteristics. An example of a patient population in which such an integral assessment can contribute to the appropriateness of care, are patients with low back pain of degenerative or unknown origin. It supports the validity and the clinical usefulness of the INTERMED when clinically relevant subgroups in this heterogeneous population can be identified and described based on their INTERMED scores. The INTERMED was utilized in a group of patients (N = 108) having low back pain who vary on the chronicity of complaints, functional status, and associated disability. All patients underwent a medical examination and responded to a battery of validated questionnaires assessing biological, psychological, and social aspects of their life. In addition, the patients were assessed by the INTERMED. It was studied whether it proved to be possible to form clinically meaningful groups of patients based on their INTERMED scores; for this, a hierarchical cluster analysis was performed. In order to clinically describe them, the groups of patients were compared with the data from the questionnaires. The cluster analysis on the INTERMED scores revealed three distinguishable groups of patients. Comparison with the questionnaires assessing biological, psychological, and social aspects of disease showed that one group can be characterized as complex patients with chronic complaints and reduced capacity to work who apply for a disability compensation. The other groups differed explicitly with regard to chronicity, but also on other variables. By means of the INTERMED, clinically relevant groups of patients can be identified, which supports its use in clinical practice and its use as a method to describe case mix for scientific or health care policy purposes. In addition, the INTERMED is easy to implement in daily clinical practice and can be of help to ease the operationalization of the biopychosocial model of disease. More information on its validity in different patient populations is necessary.