The diagnosis of CFIDS is a clinical one. It is defined as a chronic debilitating fatigue for at least six months with a reduction of at least 50% of the patient overall activities as compared to his condition prior to his illness and that there is no evidence for known causes or diseases that may be responsible for such a chronic fatigue (i.e. cancer, TB, Connective tissue disease, psychiatric disorder etc.). The existence of other minor criteria are required to establish the diagnosis such as sleep disorder, mental depression, recurrent painful lymph nodes, low grade fever, sore throats, joint pains, headaches, various skin rashes etc.

Frequently, patients give a history of recurrent respiratory infections and in about 40% of the cases an immune deficiency disorder is recognized. It is believed that this condition is associated to a chronic viral infection yet at present there is no such evidence. Most frequently treatment is symptomatic. It is important to recognize CFIDS since if an immune deficiency condition is recognized, treatment may be of a significant help to these patients with this debilitating condition.