Appendiceal mucocele is a rare clinical condition that causes distension of the appendix lumen with mucus. A seventy-three-year-old female patient presented with complaints of abdominal pain, nausea, and vomiting. Abdominal examination revealed mild tenderness, right lower quadrant pain upon palpation, rebound tenderness and muscular rigidity, and a palpable mass. Abdominal ultrasonography and computed tomography scans demonstrated a cystic lesion in the right iliac fossa, adherent to the cecum, suggesting an abdominal abscess. An emergency operation was performed, during which a diagnosis of a mucocele of the appendix was made. Surgical treatment included appendicectomy, partial resection of the ileum, and resection of the cecum. Histopathologic examination confirmed the operative diagnosis. The role of imaging and clinical approach is emphasized in the treatment of an appendiceal mucocele, especially in emergency settings.