Report is given on a 15 years old girl suffering from severe "primary" pulmonary hypertension (PPH) of the plexogenic type without underlying pulmonary parenchymal or cardiac disease. Diagnosis was established by cardiac catheterization and lung biopsy. At the same time she had clinical symptoms and laboratory signs of systemic lupus erythematosus (SLE). Looking back there had been for some years symptoms suggestive of both diseases. PPH is characterized by several histopathological criteria whereas its aetiology is unknown. A causal connexion between PPH and connective tissue diseases, especially SLE, is probable because of their repeatedly observed coincidence. Raynauds phenomenon, sometimes included in some connective tissue syndrome, and vascular alterations in PPH could be explained by sustained vasoconstrictive mechanisms caused by hyperractive pulmonary vessels. Another possible pathogenetic role relates to immune complexes causing vascular changes. It is assumed that, besides the classical pulmonary involvement, vascular changes of "primary" pulmonary hypertension themselves may represent a typical albeit rare pulmonary manifestation of SLE or other connective tissue disease.