The karyotype of a new tumorigenic Kaposi sarcoma (KS)-derived cell line, as defined by cytogenetic and fluorescence in situ hybridization (FISH) analysis is 49,XY,i(1)(q10),i(7)(p10),+i(7) (q10),+der(8)t(8;13)(p11;q11),-13,+del(14)(q22),+der(17)t(1;17)(p13;p13). Our aim was to point out some characteristics and recurrent chromosome changes probably playing a relevant role in the malignant progression of KS, by a comparison of the cytogenetic results obtained in the present study with data from the literature. The interpretation of the cytogenetic results is that KS development occurs by multiple steps: an initial reactive polyclonal cell proliferation is associated with chromosome instability; the cells in a later stage acquire clonal chromosome changes. If many chromosome changes are present, particularly 8q and 1q trisomy, 3p14-->pter deletion, 1p13, 13p14.3, 7q22, 8p11, 13q11, and 19q13 band rearrangements, KS acquires a neoplastic aggressive state.