Up to 40% of prisoner patients in a general medicine outpatient service seek medical consultation for sleep problems. This paper provides a brief overview of what is known about insomnia and its treatment from studies on non-detained patients and discusses the relevance of the findings from studies in liberty for prison health care. The clinical and ethical issues of insomnia in prison are described, followed by a summary of the existing studies on insomnia in prison. The results of the reported studies show that insomnia in places of detention should not be reduced to a secondary problem related to substance abuse and mental illness, as it appears to be an independent situational problem. Correctional health care physicians' evaluation of insomnia is insufficient. Drug prescription works well in some patients, but has a limited effect on insomnia relief in others. A clear need exists for the education of prison health care professionals on insomnia evaluation and management. Additional non-pharmacological treatment in the prison health care setting should be used more frequently. Prison health care services should develop clear guidelines based on research evidence about insomnia and which contain treatment recommendations based on the principle of equivalence of health care outside and inside places of detention.