A surgical operation to remove the spleen.

The most common reason to remove the spleen is to control severe bleeding from the organ following serious injury to either the upper abdomen or the lower ribs, both which can happen in a car accident, and is usually performed in an emergency, where it's a lifesaving measure.

It can also be removed for:
Blood diseases like Leukemia, anemia, and thalassemia
venal blood congestion
white blood cell deficiency
Gaucher's Disease
Treatment of ITP (idiopathic thrombocytopenia purpura), a blood disorder involving a deficiency of platelets.

The results vary:
Permanent improvement, such as in hemolytic anemia
a longterm remission of symptoms
provide the basis for the following treatments later, such as for Hodgkin's Disease

The longterm effects are that you can get an infection more easily. Vaccines are reccomended, as well as some surgeoins prescribe Penicillin for an indefinate period after surgery.