Background Prior studies suggest an association between complicated appendicitis and underlying appendiceal neoplasms, but the reported incidence varies widely. This study aimed to determine the incidence and predictors of appendiceal neoplasms among patients with radiographically diagnosed complicated appendicitis. Methods This study analyzed adult patients with radiologic diagnoses of complicated appendicitis (perforation, abscess, phlegmon, gangrene, or mucocele) at a tertiary center (2010–2024). To ensure diagnostic accuracy, an expert surgeon reviewed radiologic images with uncertain findings. The appendiceal neoplasm rate was calculated. Multivariable logistic regression identified preoperative predictors of neoplasm. Results Among 1690 patients with acute appendicitis, 387 (23 %) had a diagnosis of complicated appendicitis. Of these patients, 304 (78.6 %) underwent surgical treatment, whereas 56 (14.5 %) were managed nonoperatively. The rate of appendiceal neoplasms among patients with complicated appendicitis was 16.1 %. The most common tumor type was mucinous neoplasm (54 %), followed by neuroendocrine tumor (19 %) and adenocarcinoma (13 %). The incidence of appendiceal neoplasms varied significantly based on radiologic findings, with the highest rate observed in cases with mucocele (58 %), followed by abscess (18 %), phlegmon (16 %), and perforated appendicitis (12 %). After adjustment for confounders, older patient age, larger appendiceal diameter, lymphadenopathy, peritoneal enhancement, and absence of fat-stranding were significantly associated with a higher likelihood of neoplasm. Conclusion Appendiceal neoplasms were identified in 16.1 % of patients presenting with complicated appendicitis, representing a notably high incidence in this population. In the context of growing nonoperative management, radiologic and clinical predictors may need to be considered to guide decisions regarding surgery and follow-up evaluation.