Sacroiliitis describes inflammation of the Sacro-iliac joints. It is a common finding in ankylosing spondylitis (AS). It's presence may also indicate ulcerative colitis, Crohns Disease or systemic lupus erythematosus (SLE) Characteristic radiographic appearance shows erosion of the sacrum and Ilium, thickening of joint margins (sclerosis) and joint space narrowing. Infection of the sacro-iliac joint is rare but deferential diagnosis with other causes of back, pelvic and leg pain requires care. Male to female ratio is 2:1. The majority of cases occur in children and young adults. Blood cultures and MRI scanning aid diagnosis. Intravenous antibiotics constitutes the most effective treatment if infection is confirmed.