A troubling account of the unexpected impacts of treatment-based alternatives to criminal punishment. Every year, courts send hundreds of thousands of people to treatment-based programs as alternatives to traditional punishment. These alternatives—known as ‘diversion programs’—are widely celebrated as reforms that reduce the punishment of the mentally ill. But in Trial by Treatment, Mary Ellen Stitt shows that they have, in fact, expanded the reach of the criminal legal system and its power over the lives of the most vulnerable. The inner workings of diversion programs are obscure, partially by design, and data on outcomes is hard to come by. Stitt draws on two years of fieldwork in criminal courtrooms and court-mandated treatment sessions, as well as an original national dataset, in-depth interviews, and experimental survey data, to document the hidden impacts of diversion. She shows that placing mental healthcare under the control of the courts has helped to legitimize the criminalization of illness, warped treatment environments, and amplified inequalities in punishment. In vivid and humanizing detail, Trial by Treatment shows how reforms that keep power and discretion in the same hands can entrench the very problems they promised to solve.