The majority of malignancies in childhood are represented by leukemias, lymphomas or other reticuloendothelial neoplasms, tumors of the central nervous system, nephroblastomas and sarcomas. Gastrointestinal tumors represent less than 5% of pediatric neoplasms and carcinomas within this subgroup have been very rarely described, especially those arising in the stomach. In this study, we report a case of an 11-year-old boy with a signet-ring carcinoma of the stomach. The patient initially presented with respiratory symptoms which were caused by massive pulmonary lymphangiosis carcinomatosa and a peculiar microangiopathy, recently addressed as pulmonary tumor thrombotic microangiopathy. To our knowledge, this constellation has not been reported so far.