A specific chromosomal abnormality, t(2;13)(q35;q14), was discovered in five cases of advanced rhabdomyosarcoma. It was identified directly in cells that had metastasized from bone marrow in one patient and in xenografts derived from the tumors of four other patients. The translocation was not restricted by histologic subtype, but was found in cases classified as alveolar, undifferentiated, or embryonal. Cytogenetic hallmarks of gene amplification (double minute chromosomes and homogeneously staining regions) were apparent in three cases. Other frequent abnormalities included rearrangements of chromosomes lp and trisomy of chromosome 8. The absence of the t(2;13) in more than 100 cases of other pediatric solid tumors investigated in our laboratory indicates its specificity for rhabdomyosarcoma. These cytogenetic findings suggest directions for further investigation of the molecular events underlying the genesis of this tumor.