This communication concerns a fracture of the sacrum with disruption of the left sacroiliac synchondrosis and symphysis pubis, presumably produced by the force of the contractions of the uterus during labor. Although symptomatic loosening of the symphysis pubis occasionally occurs in the late months of pregnancy and rupture of the symphysis pubis during delivery is known to occur, dislocation of the sacroiliac joint is rare,1fracture of the sacrum is extremely rare, and an associated injury to the first sacral nerve root seems not to have been reported. The patient had previously complained of low back pain for 10 years and had had right dorsal, left lumbar scoliosis since adolescence. REPORT OF A CASE The patient was a 37-year-old woman, gravida 3, para 2, whose pregnancy had resulted in spontaneous delivery of a 10 lb. 10 oz. (4,819 gm.) female infant six days after the expected date of confinement,