We present the case of a female patient admitted to our University Hospital with acute abdominal pain mimicking an intraperitoneal septic condition caused possibly by acute appendicitis. CT and ultrasound scan showed a mass situated in the right iliac fossa. The patient was submitted to laparotomy and right hemicolectomy. The operative findings were suggestive of an appendiceal mucocele. The histology report revealed a low-grade appendiceal mucinous neoplasm. The patient had no clinical, biochemical or visual signs of disease recurrence 6 months postoperatively.