Epithelial proliferative lesions of the appendix are rare and have never been studied cytogenetically. We present the chromosomal banding analysis of four successfully short-term cultured samples from pseudomyxoma peritonei lesions originating from a cystadenoma of the appendix. All four sample contained clonal chromosome abnormalities. In three of them, the clone 46,XX,der(6)?del(6)(q16q21)?del(6)(q27) was found, whereas a clone with the karyotype 46,XX,t(2;17)(p21;p13),t(6;12)(p21;q13),t(12;15)(q24;q15) was detected in the fourth sample. Our findings support the view that pseudomyxoma peritonei originates by spreading from a primary mucinous neoplasm of an intraperitoneal organ rather than through mucinous metaplasia or multifocal primary neoplastic transformation of the peritoneum.