Mucocele of the appendix is characterized by distension of the appendiceal lumen due to abnormal accumulation of mucoid substance. Among the known complications of appendiceal mucocele, it is known to be unusual for the appendiceal mucocele to be a cause of ureteral obstruction. Only a few reports have been published in the English literature. We describe a case of right hydronephroureterosis secondary to appendiceal mucocele diagnosed with multidetector-row CT.