The research was conducted between March and December 1999. Discretionary life sentences in Great Britain are imposed when an offense is considered serious enough to require a very long sentence, the offender has mental instability and poses a danger to the public, and it appears that the offender will remain unstable and a potential danger for a long or uncertain time. Continuing detention after the tariff part of the sentence has been served can only be justified on the grounds that an individual's release would pose an unacceptable risk to the public. After a period of pilot work, this study collected information on 69 cases. Findings show that the quality of the decision making process was high, and decisions were reached only after careful and thorough consideration of all the available information. The measurement of effectiveness depended on the criteria used. Judging the DLP as a "court," it clearly has limited power and limited effect. Procedurally, DLP's acted consistently. The style of risk assessment was more clinical than actuarial, and was cautious. Resources were wasted in delays and deferrals, but if the positive duty on the Prison Service to move post-tariff prisoners swiftly toward release were acted on, this would save money. Recommendations for improving the operation of DLP's are offered. 2 figures and 35 references