Seventy-four acetabula from a total of 140 normal human fetuses, obtained from abortions and deaths in the prenatal period, were used. The fetuses ranged from 9.1 to 40 cm in crown-rump length and are believed to be between 12 weeks and term. Acetabula were decalcified embedded in paraffin or celloidin, sectioned, and stained using conventional histologic techniques. Sections from the superior one-quarter of the acetabulum were examined for the initial appearance and later spread of osseous tissue. Throughout the fetal period bone was present only in the floor of the acetabulum and did not extend into the socket walls. Ossification was detected initially more posteriorly in the socket floor, and at all ages, ossification was more prominent on the ischial side of the socket. Despite the lack of osseous tissue a well-formed hyaline cartilage socket was present. The fetal labrum was composed of fibrous tissue with the density of fibers increasing with age. Typical-appearing chondrocytes were detected at only the inner articular margin of the labrum. Contributing from one-fifth to one-half of the socket depth, the labrum may play a greater role in containing the femoral head at birth than it does in the mature joint. In seven acetabula, from joints that were neither subluxated nor dislocated, an area of areolar tissue with capillaries was detected at the hyaline cartilage-labrum junction. Such defects may weaken the labrum and contribute to neonatal hip instability.