Sleep disorders often remain undiagnosed and among police officers may adversely affect their health and safety and pose a risk to the public. The study found that, among police officers, sleep disorders were common and were significantly associated with increased risk of adverse health, performance, and safety outcomes. A cross-sectional and prospective cohort study of North American police officers participating in either an online or an on-site screening (n=4,957) and monthly follow-up surveys (n=3,545) between July 2005 and December 2007 was conducted. A total of 3,693 officers participated in the online screening survey, and 1,264 officers from a municipal police department and a state police department participated in the on-site survey. Of the participants, 40.4% screened positive for at least one sleep disorder, and most had not been diagnosed. Of the total cohort, 1,666 (33.6%) screened positive for obstructive sleep apnea, 281 (6.5%) for moderate to severe insomnia, and 269 (5.4%) for shift work disorder (14.5% worked the night shift). Of the 4,608 participants who completed the sleepiness scale, 1,312 (28.5%) reported excessive sleepiness. Of the total cohort, 1,294 (26.1%) reported falling asleep while driving at least once a month. Respondents who screened positive for obstructive sleep apnea, or any sleep disorder, had an increased prevalence of reported physical and mental health conditions, including diabetes, depression, and cardiovascular disease. An analysis of up to two years of monthly follow-up surveys showed that those respondents who screened positive for a sleep disorder verse those who did not had a higher rate of reporting that they had made a serious administrative error; of falling asleep while driving; of making an error or safety violation attributed to fatigue; and of exhibiting other adverse work-related outcomes including uncontrolled anger, absenteeism; and falling asleep during meetings.