We used the Insomnia Severity Index (ISI) to evaluate the prevalence and distribution of insomnia symptoms in 100 adult patients referred for laboratory evaluation of obstructive sleep apnea (OSA). Sixty-one percent met ISI criteria for a moderate to severe degree of insomnia symptoms. The distribution of insomnia symptoms did not differ by OSA severity. (C) 2009 Elsevier Ireland Ltd. All rights reserved.