The aim of this study was to determine the incidence and severity of depression in chronic pain due to different etiologies in order to detect the effects of psychological mechanisms on the severity of pain and on the pain related disability. Among the patients who admitted to the Physical Medicine and Rehabilitation Department, Department of Orthopedic Surgery, and Pain Clinic of two different Centers, 420 of those who matched the required critera and gave  consent were assigned in one of the five groups , namely miyofascial pain syndrome (MPS), fibromiyalgia (FM), osteoarthritis (OA), inflammatory arthritis (IA) and lumbar disc herniation (LDH). Beck depression inventory, visual analog scale, pain disability index and questionnairre forms developed for the study in order to note the demographic factors, were used. Depression was present in 71% of FM, 42% of LDH, 37% of IA, 31% of MPS and 16% of OA patients. Both scores were significantly lower (p<0.01) in OA group of patients. The highest scores of pain intensity and depression were detected in fibromiyalgia patients (p<0.05). In conclusion, depression seen in chronic pain patients, to some extent, might be disease specific. There was a positive correlation between pain intensity and depression in the majority of patients. PDI (pain disability index) scores increased as the severity of pain scores increased in all group of patients. PDI seems to be a very practical way of assessing disability in chronic pain patients, in which the symptoms may exceed the observable signs of an impairment since the fibromiyalgia group of patients had the highest scores.