Discharged intensive care unit (ICU) patients often recall experience vivid dreams, hallucinations or delusions. These may be persecutory in nature and are sometimes very frightening. It is possible that these memories stem from times when the patient was experiencing delirium, a common syndrome in the critically ill. Routine screening for delirium in ICU is becoming more prevalent, however, little has been published comparing the objective development of delirium (patient observations using screening tools) and patients' subjective recollection of dreams and unreal experiences in the ICU. This study describes the relationship between observed behaviour during ICU admission and the subjective memories of ICU experiences amongst 41 participants in three ICUs up to 24 months post discharge. Overall, 44% of patients (n=18) recalled dreams during their ICU admission. There was a trend to increased prevalence of dreaming (50% versus 39%) amongst the 18 patients who were delirious during their ICU admission than in the 23 non-delirious patients. Dreaming was significantly associated on logistic regression with increased length of stay (OR 1.39, 95% CI 1.08-1.79, p=0.01), but not delirium status (OR 1.56, 95% CI 0.45-5.41, p=0.49). A longer ICU stay was significantly associated with the experience of ICU dreaming. As many dreams are disturbing, we suggest providing information and counselling about delirium to patients who remain in ICU for longer periods.