Chromosomal analysis of an advanced recurrent rhabdomyosarcoma of the embryonal type was performed on cell cultures in the 9th passage of in vitro cultivation. This tumor showed a modal karyotype of 54 and was characterized by multiple numerical and structural chromosome abnormalities, all present in high frequencies. Abnormalities observed in 100% of the cells included a der(1) chromosome with a short unidentified insertion between q31 and q32; a der(1) chromosome, arising from insertion at the same breakpoint of a longer segment with a duplicated 1q31 band and translocation of 13q23----qter to 1p36, a deleted tetrasomic 13q23----qter, and a der(4) chromosome showing 1p36----pter translocated to 4p13. Other common abnormalities included trisomy of chromosomes 8, 13, and 9p, deletions of chromosomes 6, 10, 11, and 12, and presence of marker chromosomes. Characterization of the established line at the 38th passage evidenced the persistence of both the modal karyotype and all the numerical and structural abnormalities previously found. The results of this study provide further evidence of the major involvement of alterations in chromosome 1 in the progression of rhabdomyosarcoma.