The fibrositis syndrome represents a clinically definable entity, which is characterised by spontaneous pain, especially in the lumbar and cervical region, and more rarely in other movable parts, multiple tendomyosis, tendinitis and insertion tendinitis, as well as a wide variety of functional syndromes, vegetative symptoms and psychological disturbances. The course of the illness is rather variable; its commencement can be slow to develop or acute, initially presenting a localised clinical picture similar to a lumbar or cervical condition, and gradually, or in jumps, showing a deterioration accompanied by a generalisation of complaints. Various factors are probably instrumental in triggering off the fibrositis syndrome. The most important ones are emotional stress whereby symptoms of fear, depression, etc. lead to muscle tension and insertion tendinitis. Somatic factors such as malposition of the spinal column, may also contribute towards the manifestation of the clinical picture. The so-called secondary fibrositis syndromes should be defined from the point of view of differential diagnosis; they can develop within the framework of inflammatory rheumatic conditions, through infections and endocrinopathy. Differential diagnosis is very difficult considering depression alongside pain in the movable parts and "psychogenic rheumatism". Smooth transitions are in existence. Polymyalgia rheumatica and polymyositis, which produce similar clinical pictures, must be differentiated from the fibrositis syndrome.