A 24-year-old Japanese man presented with dyskeratosis congenita (DC, Zinsser-Cole-Engman syndrome) complicated by non-cirrhotic portal hypertension, signet ring carcinoma of the rectum andPneumocystis carinii pneumonia. At the age of 9 years, he was diagnosed as having DC on the basis of typical clinical manifestations including atrophic lingual papillae, hyperpigmentation of the skin, thrombocytopenia, and ophthalmological abnormalities. A few years later pancytopenia and splenomegaly developed. At 24 years, signet ring carcinoma of the rectum was detected but could not be resected because of the severity of the pancytopenia. Death was due to respiratory failure fromP. carinii pneumonia. At autopsy the case illustrated several unique findings for DC, including non-cirrhotic portal hypertension, atrophy of frontal lobe and markedly slender folia of the cerebellum and superimposed infections with herpes zoster virus andP. carinii. Striking lymphocyte depletion and atrophy of lymphoid parenchyma in lymph nodes, tonsils, spleen, gastrointestinal tract, or thymus were seen histologically. The morphological picture supports the suggestion that there is a defect in the cell-mediated immune system in patients with DC, although immunoglobulin levels in the blood are normal. The cell-immune deficiency is a major factor in the poor prognosis.