Occupational exposure to ionizing radiation causes chromosomal damage. Some of the damaged cells show a large number of aberrations such as dicentrics, polycentrics, rings and numerous acentric fragments. This paper describes an analysis of the frequency of dicentric chromosomes and acentric fragments in 1260 subjects occupationally exposed to X-rays and 241 controls. Special attention was paid to the incidence of multi-aberrant cells. The 3 year cumulative dose was a significant predictor for all analyzed aberrations. The duration of exposure was a highly significant predictor of the frequency of rogue cells, but not of acentrics and dicentrics. Age and sex were not found to be significant predictors of the analyzed aberrations.