BACKGROUND: Effective management of sleep pattern disturbance begins with accurate assessment of the patient's sleep and wake states. OBJECTIVE: The purpose of this study was to validate staff nurses' observations of sleep and wake states among critically ill adult patients, using polysomnography. SAMPLE AND SETTING: The sample consisted of 21 adult patients with multisystem diagnoses in a 10-bed medical intensive care unit in a 540-bed acute care teaching hospital. METHOD: Each staff nurse caregiver observed a single patient for the entire data collection period of 4 hours, with a total of 15 nurses participating in the study. A total of 340 observations were made, with the possibility of 17 observations per patient. Nursing observations were made every 15 minutes on each patient and compared to the actual patient state as measured by polysomnography. RESULTS: Nurses' assessments were correct 81.9% of the time. CONCLUSIONS: There is some basis for using staff nurses as observers of sleep and wake states. Increased credence can be placed on nursing assessments and diagnosis of sleep pattern disturbance, resulting in more timely and effective management of the problem.