Henoch-Schonlein purpura (HSP) is an autoimmune disorder unusually found in children between the ages of 3 and 15. The diagnosis is often made on clinical grounds. Patients often have a raised, purplish rash, often involving the buttocks. Arthritis is very common. Patients often have abdominal symptoms such as abdominal pain, nausea and vomiting and there may be microscopic evidence of blood in the stool. Examination of the urine will often reveal evidence of protein or blood in the urine signifying renal disease. If a diagnosis is still unclear, biopsy of a skin lesion is often diagnostic. A kidney biopsy may be required in patients with severe kidney problems.