Abdominal pain is common feature of Henoch-Schonlein purpura, which may mimic appendicitis, leading to unnecessary laparotomy. Accordingly, the diagnosis must be confirmed by ultrasonography or computed tomography scan before laparotomy is performed. The authors report a case of simultaneous occurrence of Henoch-Schonlein Purpura and gangrenous appendicitis in an 18 year-old boy. The patient was admitted with abdominal pain, cramps, and mild dehydration. He also complained of small reddish purple on his lower limbs, bilateral knee pain, low-grade fever, as well as bloody stools. The symptoms subsided completely. Eight days later, he returned with nonbloody, nonbilious emesis, abdominal cramps, and right lower quadrant abdominal tenderness. Abdominal ultrasound evaluation was performed to rule out an intussusception but demonstrated appendiceal dilatation with a possible appendicolith without any evidence of intussusception. A laparotomy was undertaken, and appendectomy was performed for gangrenous appendicitis. Simultaneous occurrence of Henoch-Schonlein purpura and acute appendicitis is rarely observed. Clinical features of the patients may mislead the clinicians, resulting in delayed diagnosis or misdiagnosis. The use of ultrasonography and computed tomography scan would confirm the diagnosis before surgery.