Clonal chromosome aberrations were detected in 8 short-term cultured malignant peripheral nerve sheath tumors (MPNST). Seven had a near-triploid chromosome number and I was in the hyperhaploid-hypodiploid range. No recurrent structural rearrangements were found; the bands most frequently involved (3 tumors) were 7p11, 12p13 and 14q11. The most common numerical changes were loss of a sex chromosome (all tumors) and loss of at least 1 copy of chromosomes 8, 16 and 22 (4 tumors). Pooling our data with those on the 20 previously published MPNST with abnormal karyotypes, we found that the chromosome number has often been in the triploid range (12 tumors), with stem line variation between 34 and 270. All chromosome arms, except 22p and the Y chromosome, were involved in recombinations. The most frequently rearranged bands were 7p22 (6 tumors) and 1p21, 7p11 and 14q11 (5 tumors each). Most numerical and unbalanced structural aberrations have led to loss of genetic material, in particular from Xq26-qter (13 tumors); 11q22-qter and 13p (12 tumors); 9p22-pter, 11p13-pter, 17p and 17q11-21 (11 tumors); 1p22-32 and 1p34-pter (10 tumors) and 6q25-qter and chromosome 16 (9 tumors).