Retrospective surveys were carried out on two groups of patients who had survived a stay of at least 48 h in an Intensive Therapy Unit. One group had been kept in a unit without windows, and the other in a similar unit with translucent but not transparent windows. Survivors from the windowless unit had a less accurate memory of the length of their stay, and were less well orientated in time during their stay. The incidence of hallucinations and delusions was more than twice as high in the windowless unit. The phenomenon of depersonalisation in the face of life-threatening danger is described and discussed.