Reducing recidivism is a central goal in the treatment of sex offenders. In Europe, there is an increased interest in using the polygraph ("lie detector") as a tool in the treatment and risk assessment of convicted sex offenders. This interest originated from optimistic reports by American clinicians who argued that polygraph testing in the treatment of sex offenders is akin to urine analysis in the treatment of drug addiction. In this article, we critically examine the validity and utility of post-conviction sex offender polygraph testing. Our review shows that the available evidence for the claims about the clinical potential of polygraph tests is weak, if not absent. We conclude that portraying post-conviction polygraph testing as analogous to urine analysis is inaccurate, misleading, and ultimately, risky.