Treatment-seeking opioid-dependent individuals frequently report sleep-related problems. This study provides a detailed assessment of sleep duration and quality in this population, including their effect on daily functioning and relationship to psychiatric severity and drug use. Samples of newly admitted patients to opioid agonist maintenance treatment (n = 113) completed a series of questionnaires to assess sleep functioning, psychiatric severity, and drug use due to sleep problems over the past 30 days. The results showed that study participants reported considerable sleep-related difficulties that had little effect on their appraisals of daily functioning. Nevertheless, sleep problems were associated with psychiatric distress, and those reporting substance use specifically to increase or decrease sleepiness endorsed more sleep problems and lower levels of daily functioning. Overall, these results replicate and extend previous work showing poor sleep functioning in this population and show that sleep problems are associated with variables that often have an adverse impact on substance abuse treatment outcome.