We tested the value of the radiographic indexes in 16 patients with the diagnosis of pulmonary hypertension of unknown etiology. The index PL/T (lung-lobe-thoracic) was abnormal in 62.5%, the Osawa-Kanemoto index (DPA(T/2] was also abnormal in 62.5% of the cases, the r/h index (which measures the ratio right pulmonary artery thickness/right lung field) was abnormal in 81% of the cases. There was no relationship between the above mention indexes and the pulmonary artery pressure. Seven of the 16 patients displayed a new radiographic image that we have named "reticulo-vascular pattern", this radiographic sign may be important in the diagnosis of primary pulmonary hypertension.