Giant cell interstitial pneumonia (GIP) is a very uncommon respiratory disease. We report a juvenile patient with GIP aged 15 years. Although he has a negative past history of direct exposure to hard metals, we could not exclude possible exposure in very small amounts through his parents. Microscopic examination of lung biopsy specimen obtained by video-assisted thoracoscopy revealed marked cellular interstitial infiltrates and prominent intraalveolar macrophages as well as giant cells showing cellular cannibalism. Analysis of the biopsied lung tissue for cobalt and tungsten was negative. Clinical symptoms, laboratory, and radiological findings improved markedly after treatment with corticosteroids. To our knowledge, only eleven cases of GIP have been reported in Japan. Although possible exposure to hard metals was identified in 9 of the 11 reported cases, there is no clear dose-dependent relationship with onset and prognosis. The average age at onset was 46.2+/-15.0 years. Our patient is the youngest case of GIP reported in the world.