After Susan's death from toxoplasmosis, Tommy was placed in foster care. It is later revealed that Susan was HIV-positive long before Lisa was born and may have passed on the disease to him. When Tommy is tested for HIV, he puts up a struggle and kicks Stabler in the ribs, breaking two of them. His attorney puts a halt on Tommy getting tested.
Greylick and Stabler press charges against Tommy for assaulting Stabler in order to test him for HIV. Later, Stabler drops the charges after they fail, but brings him to a young cancer patient who convinces Tommy to get tested. At the end of the episode, it's revealed that Tommy has HIV. (SVU: "Retro")