Background: Interval appendectomy after acute appendicitis with lump formation (phlegmon) remains controversial. We conducted this study to determine the risk of recurrent appendicitis following initial non-operative treatment for appendicitis, and evaluate factors associated with recurrence. Secondarily, we evaluate the efficacy of interval appendectomy versus no appendectomy. Materials and Methods: Patients who received conservative treatment for appendicitis with lump formation were prospectively studied from June 2006 to June 2008. These patients were followed for recurrence of appendicitis. Results: Of 763 patients with acute appendicitis some 220 patients had lump formation (28.8%). Median age was 28 years. Conservative treatment was successful in 213 (96.8%) patients. The rate of recurrence was 13.1%, all occurring within six months after the index admission. Mean follow-up was 26±18 months. Conclusion: Conservative treatment of appendicitis with lump formation is efficient and the recurrence rate is low. Routine interval appendectomy after initial conservative treatment for lump formation is not a cost-effective intervention and not recommended.