As part of the sixth framework EUMHADIE (Measuring Health and Disability in Europe: supporting policy development), the International Classification of Functioning, Disability and Health (ICF) was employed by 12 EU facilities (among them six clinical settings). A cross-sectional study of patients (n = 1,019) with eight different chronic conditions (musculoskeletal conditions rheumatoid arthritis, osteoporosis, osteoarthritis, low back pain, multiple sclerosis, Parkinson's disease, migraine, stroke, depression, bipolar disorder, and traumatic brain injury) was conducted. The Department of Rehabilitation Medicine of the First Faculty of Medicine and General Teaching Hospital in Prague participated in this project with 100 patients after TBI (traumatic brain injury) and 100 patients with MS (multiple sclerosis). Patient evaluation was performed by qualified health-professionals (trained on ICF courses) who completed a checklist composed according to ICF categories. Every patient then answered socio-demographic questions common to all centres and marked specific scales assessing the details of the disease. With the help of health professionals or students, the patients filled in the WHODAS II standardized quality of life questionnaires (WHO Disability Assessment Scale) and SF-36 (Short Form Measure of Generic Health Status) compiled along ICF guidelines. The study analyzed the structure of causal factors in terms of Activities (Capacity) and Participation (Performance). The authors would like to draw attention to the importance of ICF as a classification and, further, they would like to suggest the use of ICF in clinical and epidemiological studies.