The pursuit of purity is a central theme and the final line of The Basketball Diaries: “I just want to be pure” (211). Purity is the absence of filth, trauma, and immorality, with Jim’s actions being its antithesis. Jim self-sabotages his desire for purity by taking drugs and becoming addicted to them. He spends most of his time doing drugs and committing crimes to obtain more drugs (or occasionally for fun). While most people would consider doing drugs a bad habit, Jim uses them to feel pure. He discusses the matter with his friend Brian: When Brian remarks that a person high on heroin curls up like a fetus, Jim agrees that this is the entire point of doing so. For Jim, heroin provides a return to innocence, a state before society corrupted and traumatized him. LSD provides a slightly different feeling, but one still related to purity; he uses it to lose himself and connect with nature.

Teenagers often experience a loss of morality and innocence as they test the waters of adulthood. Jim remarks on this phenomenon, noting that he is breaking many rules he made for himself as a child.