Chromosome 18 was analysed using a banding technique and fluorescence in situ hybridization (FISH) in 13 pancreatic carcinoma samples. The cytogenetic analysis revealed that chromosome 18 abnormalities were present in all cases and that several different rearrangements, such as translocations, deletions, dicentrics and ring chromosomes, were often found together. FISH mapping using 18q YAC probes showed that all tumours had lost at least one copy of 18q and that 18p was over-represented in 6 of the 13 cases. Furthermore, out of 13 identified deletion breakpoints on 18q, 11 were mapped to 18q11. The clustering of breaks close to the centromere indicates that loss of genes in bands 18q11 and 18q12, in addition to those located in 18q21, e.g. DPC4 and DCC, are important in the development of pancreatic tumours.