Local and regional musculoskeletal discomfort and pain in the shoulder girdle or upper extremities are often reported, especially in the working population. In this review we describe the most important problems and factors when classifying musculotendinous pain in the upper extremities and shoulders. This includes an analysis of how four common diagnoses (wrist tenosynovitis, lateral epicondylitis, rotator-cuff tendinitis, myofascial pain syndrome) fulfil basic criteria of validity. It is evident that there are some serious problems regarding the validity of the current classification of the conditions. Clinical criteria are often poorly defined and the reliability insufficiently tested. The relationship to objective pathoanatomic or physiological findings seems inconsistent. Although magnetic resonance and ultrasonographic imaging are promising, they are still only preliminary methods for evaluation of tendon and connective tissue structures. The prognosis with and without treatment also seems heterogeneous and can vary between studies. A generally accepted terminology is lacking in the pathogenetically complex regional muscle pain conditions.