There is pseudo-widening of the symphysis pubis caused by severe localized mineral loss and erosions in the subchondral bone. Sclerosis is present in the pubic bones proper. These changes are analogous to those that occur in the sacroiliac joints. This 12-year-old boy has juvenile-onset ankylosing spondylitis and is positive for the HLA-B27 antigen. Similar changes may be seen in the teenager and adult. These findings are not limited to ankylosing spondylitis.