Clinical and immunophenotypic (IP) data are presented on three children with choroid plexus (CP) tumors. Two children ages 0.2 and 2 years old with histologically proven malignant tumors had subtotal tumor resections and were treated with ten monthly cycles of eight-drugs-in-1-day chemotherapy without radiation therapy (XRT). Both are free of tumor 4 and 7 years later. The literature on survival of children with CP carcinomas after chemotherapy and XRT is reviewed. Monoclonal antibodies to 17 neuroectodermal, neuronal, glial, and leukocytic markers on frozen sections were used to IP the two malignant tumors and a CP papilloma. All tumors expressed two neuroectodermal markers (PI-153/3 and UJ 223.8), cytokeratin 19, and a neural and leukocyte marker (Thy-1). Two of three expressed neurofilament protein (NF-H) and glial fibrillary acidic protein (GFAP) and one expressed NF-M and common leukocyte antigen. None had strong expression for the panneuroectodermal antigen UJ13/A. There was variable expression of the other markers. The most common IP profile for CP tumors (cytokeratin 18+, PI-153/3+, Thy-1+, UJ 223.8+, and GFAP+ and UJ13A-, UJ 127.11-, and NF-L-) is discussed in the context of the current knowledge of the ontogenetic origin of the CP. It was concluded that chemotherapy for malignant CP tumors can be associated with long-term survival in young children and that the unique IP profile of CP tumors with coexpression of three intermediate filaments suggests new and provocative evidence of their cellular complexity and heterogeneity.