Tissue samples from a malignant melanoma of the anal canal and its local metastasis were short-term cultured and analyzed cytogenetically. Complex chromosome aberrations were found in the primary tumor, yielding the karyotype 49-50,X,-Y,der(1)t(1;13)(q44;q12),+der(2)t(2;8) (q31;q12),der(6)t(5;6)(q13;q21),+del(6)(q12q21),+7, der(8)t(6;8)(p12;p21),del(11)(p11),der(11)t(11;12) (p15;q24),der(15)t(6;15)(p21;p11-13),+der(20)t(1;20) (q12;q13),der(22)t(11;22)(p11;p11)[34]/88-100,idemx2[3]. In the local metastasis, the same near-tetraploid abnormal clone was detected, indicating that the cell population was clonally stable during tumor progression. This is the first malignant melanoma of the anal canal that has been cytogenetically characterized.