Encouraging disclosure of information is an essential task of probation intervention with sex offenders. Here, Daniel Wilcox, Dan Sosnowski and David Middleton argue that the polygraph, or lie detector, can help to achieve this aim, and play an important role in assessing risk, treating and managing sex offenders on probation or licence. They examine the use of the polygraph in the USA, and give some early reflections on the first UK polygraph trial, held in the West Midlands Probation Service area. The results suggest that workers were able to obtain more detailed information about index offences, further diclosures of past sexual offending, and more information about short-term risk and non-compliance with conditions of probation orders.