We report the results of a morphological analysis of 60 pulmonary biopsies gathered from a multi center study, organised by the clinico-pathological research group on Wegener's Disease under the auspices of the French Language Society of Thoracic Medicine. Forty of the sixty cases analysed were retained after indexing the histological aspects in order to specify their diagnostic value. Two groups of lesions were distinguished, which had different significance. Group A: These include the three major diagnostic criteria, which reinforce one another as they associate: 1) The polymorphoneutrophil microabscesses with limited central necrosis or an extended necrosis like the contours of a relief map. 2) An angiitis (arteries, veins, capillaries) with eccentric focal parietal crescent-shaped microabscesses. 3) Polymorphous granulomas with giant cells. Group B: In this group are the minor morphological observations (table II) of a lesser value and significance. 1) Acute or chronic lesions with alveolar haemorrhage, endogenous lipid pneumonia, xanthomatous granulomas, an organising pneumonia with an alveolitis. 2) Bronchial lesions: Bronchitis and necrotising bronchiolitis, which is more rarely follicular. 3) Sero-fibrinous or infiltrative neutrophil pleural lesions with focal microabscesses, elastolysis and elastophagia with giant cells in the elastic lamina. Thirteen cases presented with misleading lesions, which was a possible source of diagnostic error and led to a discussion of several associated disorders (Goodpasture's syndrome, and collagen disorder syndrome) or there may be systemic angiitis (Giant cell or lymphocytic) or also systemic or tissue eosinophilia (Churg-Strauss syndrome, bronchocentric granulomatosis) or necrotising bronchitis (atrophic polychondritis) or other forms of nodular interstitial fibrosis, such as histiocytosis X. We would like to stress the great polymorphic variation of the lesions and the difficulties which confront pathologists in the diagnosis of Wegener's Disease, above all when it is localised to the lung. There is value in finding at least one major diagnostic criteria which is associated with a minor criteria and with the help of the C.ANCA levels may lead to a narrow clinicopathological correlation and allows for a fairly precise approach to the diagnosis and identification of early or unusual lesions and thus to the early treatment of patients before irreversible renal failure appears.