Background: Ureteral obstruction is rarely caused by extrinsic compression from the appendix. In addition, mucinous neoplasms of the appendix are rare, found incidentally in 0.2%-0.7% of appendectomy specimens. Case Presentation: We present an unusual case of ureteral obstruction caused by a large appendiceal mucocele. An asymptomatic 53-year-old caucasian male patient, known for recurrent nephrolithiasis, was referred for management of bilateral nephrolithiasis. A noncontrast CT scan found an atrophic kidney with an obstructive 1.8 cm right midureteral stone above a 9 × 4.3 cm appendiceal mucocele compressing the right midureter. Although the impacted ureteral stone was extracted with retrograde ureteroscopy and holmium laser lithotripsy, the appendiceal mucocele was resected by laparoscopic appendectomy. Final pathology analysis revealed an unperforated low-grade appendiceal mucinous neoplasm of 13 cm without lymphovascular invasion. Since the whole mucocele was completely excised, it did not require any further follow-up. Postoperative CT scan demonstrated stone-free status on the right side with residual mild right hydroureteronephrosis. A diuretic renal scintigraphy showed a nonobstructed right kidney with a chronically dilated pelvicaliceal system and a 34% differential function in the right kidney. Follow-up for up to 2 years postoperatively demonstrated that his diuretic renal scan did not show deterioration of the differential renal function, indicating that there was no significant obstruction. Conclusion: This is the fourth reported case of appendiceal mucocele causing extrinsic ureteral obstruction, and the secondary urinary stasis contributed to formation of a large midureteral stone and cortical renal atrophy. This case demonstrates the importance of the work-up and management of obstructive ureteral stones before definitive management of appendiceal mucoceles.