Background: In this paper we present a case of perforated mucinous neoplasm of the appendix. Diagnosis and treatment of this rare condition are briefly discussed. Material and methods: A 42-year-old patient admitted to the General Surgery Clinic for elective surgery of left-sided inguinal hernia. In the postoperative period, severe pain in the lower abdomen persisted – qualified for laparotomy, during which an appendix tumor and a large amount of gelatinous bloody contents in the right lower abdomen were found. The appendix was removed and the peritoneal cavity was cleaned in the content. Histopathological examination revealed low grade appendiceal mucinous neoplasm (LAMN) pT4a NX M1b. No angiovasia or nerve trunk infiltration were found. At the top of the appendix a perforation with mucus around was noted. Postoperative course was uncomplicated. The patient was referred to a peritoneal carcinomatosis center where a right hemicolectomy with HIPEC therapy was performed. Results: Mucous neoplasms of the appendix of low grade (LAMN) are rare tumors. Conclusions: Mucous neoplasms of the appendix of low grade (LAMN) are rare tumors. The treatment of choice is surgical excision. The most serious complication of LAMN is a rupture with the escape of mucus into the peritoneal cavity.