Radiographs of vertebral structures of 10,377 sockeye, 4,403 chum, and 4,777 pink salmon collected in 1958 to 1962 were examined to determine the frequency of occurrence of abnormal vertebrae in wild populations of mature Pacific salmon. Various types of deviations from the orderly processes of development or segmentation that resulted in abnormal structures were classified as fusions or abnormalities. The frequency of occurrence of abnormalities in the vertebral column was tabulated by species, sampling locations, and year of sampling. Abnormalities were found in the vertebral columns of 2.8% of the sockeye, 3.3% of the pink, and 2.9% of the chum salmon. Differences in frequency of occurrence of abnormalities among the species were not statistically significant. In sockeye salmon, 47% of the abnormalities were in the caudal region and 42% in the abdominal region; in pink salmon, 39% were in the caudal and 49% in the abdominal region.