THE patient whose case introduces this paper, a Mr. E. H., white, aged 55, married, a foundry worker, weight 150 pounds, sustained an injury to the coccyx on May 25, 1929. In the course of his duties, he fell from a step-ladder, landing on his buttocks on a wooden box, a corner of which directly struck the coccyx. He experienced immediate pain and was referred to the company physician, who found, the following morning, by rectal examination, an unevenness of the anterior surface of the coccyx, and pain upon pressure, both externally and in the rectum. He diagnosed a dislocation and referred the patient to me for roentgen examination. Lateral projection revealed a forward luxation of the first coccygeal segment, which was displaced a distance almost equal to its own thickness, the rest of the coccyx being symmetrically curved. The outlines of the upper coccygeal and the last sacral element indicated that no bony fusion had existed and the remaining segments showed distinct spacing, as if separated by cartilage. The antero-posterior view gave no hint of the luxation, but showed a vertical line in the first segment that was suspicious of fracture, without displacement. The cornua were not visible; the transverse processes were very rudimentary. Four coccygeal segments were plainly registered, the distal one possibly representing a fusion of two rudimentary elements. The contour of the sacrum and coccyx described a normal curvature, except for the luxated first segment, and there was no lateral deviation. On May 27 the attending physician reduced the dislocation, by intrarectal digital pressure, with the patient in a kneeling position. Bowel movements were painful for only a few days, but for three or four weeks the patient complained of an aching sensation. He resumed work in eight weeks. On October 5 he was referred for another roentgen examination, at which time he said he was free from all pain and ache, except after long automobile rides. Digital examination was painless. The roentgen films showed the same luxation of the first segment, with apparent callus formation anteriorly at the sacrococcygeal junction. Medical literature shows few and brief allusions to roentgen examination of the coccyx. Careful search failed to reveal any article in roentgenologic journals, and the text-books give little or no information. George and Leonard (1), in their recent volume, illustrate a case of anterior luxation. Jones and Lovett (2) say: “X-ray may or may not be reliable in this region and the antero-posterior view shows only lateral displacement. To obtain satisfactory definition in a side X-ray is, of course, difficult, but often possible with a highly perfected technic.” Letters written to 94 roentgenologists brought few helpful replies. Coccyx (plural coccyges) is a word derived from the Greek, meaning a “cuckoo,” probably because of a fancied resemblance to a cuckoo's beak.