Human neuroblastoma cells often are monosomic for the distal portion of 1p (1p36). We report that the deleted 1p material in cells of neuroblastoma lines is preferentially replaced by material from chromosome 17, resulting from an unbalanced 1;17 translocation. Chromosome 17 often acquires instability, followed by the integration of fragments into various marker chromosomes. As a consequence, 17q material can increase over 17p material. The nonrandom frequency of 1;17 translocations appears to indicate an as-yet-undefined contribution to neuroblastoma development.