This study aimed to describe the quality of sleep of non-intubated patients and the night-time nursing care activities in an intensive care unit. The study also aimed to evaluate the effect of nursing care activities on the quality of sleep. An overnight polysomnography was performed in 21 alert, non-intubated, non-sedated adult patients, and all nursing care activities that involved touching the patient were documented by the bedside nurse. The median (interquartile range) amount of sleep was 387 (170, 486) minutes. The portion of deep non-rapid-eye-movement (non-REM) sleep varied from 0% to 42% and REM sleep from 0% to 65%. The frequency of arousals and awakenings varied from two to 73 per hour. The median amount of nursing care activities was 0.6/h. Every tenth activity presumably awakened the patient. Patients who had more care activities had more light N1 sleep, less light N2 sleep, and less deep sleep. Nursing care was often performed while patients were awake. However, only 31% of the intervals between nursing care activities were over 90 min. More attention should be paid to better clustering of care activities.