Examination of the sacroiliac joints of complete skeletons from the Hamman-Todd Human Osteological Collection of the Cleveland Museum of Natural History found that male skeletons are distinguished by a preliminary partial or full extra-articular bridging of the sacroiliac joint, especially when located at the upper part of the joint. This SIB condition does not vary by ethnicity or geographic origin; however, the SIB condition is more prominent in older individuals. Reasons for the prevalence of SIB among males compared with females, as well as for the different appearance of the bridging in males and females, have not been determined. A reasonable hypothesis for testing pertains to gender-based hormones involved in bone modeling related to childbirth for women and the need for the sacroiliac joint to bear greater physical stress and heavier body trunk and upper limbs in men. The skeletons examined were of individuals who died during the first half of the 20th century. Age at death, sex, ethnic origin, and cause of death had been documented for each individual. The collection consisted of 1,518 White males, 837 Black males, 216 White females, 272 Black females, and 2 females of Asian descent. The ilium and sacrum of each skeleton were examined for the presence of new bone formation and bridging/fusion in/across the anterior part of the joint. Full and/or partial bridging between the sacrum and the ilium was recorded along with the beginning of new bone formation over the sacroiliac joint. The extent and location of the bridging was determined by dividing the anterior margin of the sacroiliac joint into six areas. 7 figures, 2 tables, and 13 references