Mucocele of the appendix is a relatively rare disease characterized by a cystic dilatation of the appendiceal lumen with stasis of mucus inside. Appendiceal mucocele with a cutaneous fistula is an extremely rare clinical entity, only four such cases being described in the medical literature. We report an additional case of cystadenocarcinoma of the appendix with spontaneous cutaneous fistula. The patient is an 80-year old woman, who originally presented with a skin ulcer in the right lower abdominal quadrant with mucus discharge during the last month. Abdominal ultrasonography and computed tomography demonstrated cystic mass with mixed echogenity and density originating from the appendix, involving the abdominal wall, without signs of ascites or metastasis. A right hemi-colectomy, lymphadenectomy and resection of the skin fistula was performed. The histological findings revealed moderately differentiated mucinous cystadenocarcinoma of the appendix. The postoperative period was uneventful and the patient discharged on the 11th POD. During 12 month follow-up period the patient is free of disease recurrence. The authors present the literature review, diagnostic features and the treatment policy of this extremely rare condition.