Spontaneous splenic rupture (SSR) is a rare but potentially lethal complication of infectious mononucleosis (IM). Because the inflamed spleen is usually enlarged, congested, and friable, emergency splenectomy is recommended. We describe the conservative management of a SSR in a 16-year-old boy with IM. A pigtail catheter was inserted under ultrasonographic guidance and left in place for 36 h. This allowed the successful evacuation of the hematoma without compromising the splenic parenchyma.