A variety of miscellaneous conditions affect the appendix, both as incidental findings and as causes of clinical signs and symptoms that often mimic appendicitis. Congenital abnormalities of the appendix are rare; the two most commonly reported are congenital absence and appendiceal duplication. Diverticular disease may be an incidental finding, but when inflamed, can be clinically confused with appendicitis. Endometriosis of the appendix, which usually occurs in the setting of generalized gastrointestinal endometriosis, often presents as acute appendicitis, but may present as intussusception, lower intestinal bleeding, and, particularly during pregnancy, perforation. Peritoneal endosalpingiosis often involves the appendiceal serosa and occasionally the wall but has no clinical manifestations in contrast to endometriosis. Vasculitis may be either isolated to the appendix or part of a systemic vasculitis, most often polyarteritis nodosa. Neural proliferations of the appendix include lesions associated with von Recklinghausen's disease, as well as mucosal and axial neuromas that are theorized to progress to fibrous obliteration of the appendix. Mesenchymal tumors of the appendix are most often of smooth muscle type, usually leiomyoma but rarely leiomyosarcoma; nonmyogenic neoplasms such as gastrointestinal stromal tumor, granular cell tumor, Kaposi's sarcoma, and miscellaneous other curiosities occur rarely. Lymphoma affects the appendix exceptionally; in children, Burkitt lymphoma is most common whereas in adults, large cell lymphomas and low grade B-cell lymphomas predominate. Secondary involvement of the appendix by leukemia has been reported. Secondary involvement of the appendix by carcinomas of the female genital tract, particularly ovary, and diverse other sites are in aggregate common but only rarely a clinical or pathological difficulty. Occasionally, however, appendiceal neoplasia that is secondary from another site may dominate the clinical picture and lead to potential pathologic misdiagnosis as primary appendiceal disease.