Abstract Background Low-grade appendiceal mucinous neoplasm (LAMN) is a precursor lesion for pseudomyxoma peritonei (PMP), which, if treated suboptimally, may later disseminate throughout the abdominal cavity. The role of cytoreductive surgery for these relatively early lesions is unclear. Methods Clinicopathological details and treatment outcomes of patients with a LAMN and disease limited to the appendix or immediate periappendiceal tissues, referred to a national treatment centre between 2002 and 2009, were evaluated prospectively. Results Of 379 patients with a diagnosis of PMP, 43 (median age 49 years) had LAMNs localized to the appendix and periappendiceal tissue. Thirty-two patients initially presented with symptoms of acute appendicitis or right iliac fossa pain. Two distinct lesions were identified: type I (disease confined to the appendiceal lumen) and type II (mucin and/or neoplastic epithelium in the appendiceal submucosa, wall and/or periappendiceal tissue, with or without perforation). Type I lesions were managed by a watch-and-wait surveillance policy with serial measurement of tumour markers and computed tomography in 14 of 16 patients. Seventeen of 27 patients with type II lesions underwent risk-reducing cytoreductive surgery and hyperthermic intraperitoneal chemotherapy with low morbidity. After a median follow-up of 40 months, there was no disease progression in either treatment pathway. Conclusion This study identified two LAMN subtypes. Type II lesions have pathological features of increased risk for dissemination and should be considered for risk-reducing cytoreductive surgery.