Although uncommon, primary appendiceal neoplasms often result in clinical symptoms that may lead to abdominal imaging. Acute appendicitis from luminal obstruction is the most common manifestation for most tumor types. Other manifestations include intussusception, a palpable mass, gastrointestinal bleeding, increasing abdominal girth (from pseudomyxoma peritonei), and secondary genitourinary complications. Asymptomatic appendiceal neoplasms may be discovered incidentally. Mucoceles from either benign or malignant mucinous neoplasms represent the majority of appendiceal tumors detected at imaging but are the least likely to manifest as appendicitis. Pseudomyxoma peritonei is a common manifestation of mucinous adenocarcinoma. Colonic-type (nonmucinous) adenocarcinoma of the appendix is much less common than mucinous tumors and typically manifests as a focal mass without mucocele formation. Carcinoid tumor is the most common appendiceal neoplasm but is less often detected radiologically because it is typically small and relatively asymptomatic. Goblet cell carcinoid tumor and non-Hodgkin lymphoma of the appendix are rare and usually infiltrate the entire appendix. Cross-sectional imaging, particularly computed tomography (CT), is effective in the evaluation of these neoplasms. CT appears to be the modality of choice whenever an appendiceal mass is suspected. CT will help rule out or confirm an appendiceal tumor and may suggest a more specific diagnosis.