Malignant rhabdoid tumors are highly aggressive childhood tumors. Recently, all of the malignant rhabdoid tumors, whatever their location, have been related to the inactivation of the hSNF5/INI1 gene. A subset of cerebral tumors, associated with malignant rhabdoid tumors or isolated ones arising in siblings, showed similar molecular alterations. We report for the first time in monozygotic twins a congenital disseminated malignant rhabdoid tumor in one twin and a cerebellar tumor mimicking a medulloblastoma in the other. Molecular analysis revealed similar alterations for both tumors: a deletion of exon 7 of the hSNF5/INI1 gene in one allele, and a point mutation in the same exon in the other, suggesting a common genetic pathway. Analysis of constitutional DNA revealed a germline mutation. These findings are in favor of a common etiology for rhabdoid tumor and a subset of brain tumors developing in infancy.