Recently, the importance of the ICU environment as a potential modifiable factor for improvement of patient care has become more clear. In this review, we describe the effects of light and noise exposure on ICU patients. In ICU patients circadian rhythms and sleep are severely disturbed, which may increase the risk of delirium. Realignment of circadian rhythmicity by means of artificial light therapy has not been shown to reduce the incidence or duration of delirium. Prudent use of nighttime light may be a first step in improvement of patient sleep. Eye masks appear to improve sleep although they are only applicable for a selected group of patients. Noise levels in the ICU are above recommended standards. Negative effects include disturbances of sleep, as often encountered in ICU patients. Staff activity and talking contribute substantially to the total acoustic energy, providing opportunities to adapt behaviour and/or workflow in order to reduce noise pollution.