It is not uncommon for patients in intensive care units (ICUs) to suddenly and unexpectedly present what is known as acute ICU syndrome. This syndrome appears independently of the patient's situation and diagnosis. The aim of the present study was to determine the incidence of this nursing diagnosis in our department, to identify the possible environmental factors that could contribute to its appearance and to evaluate nursing interventions to resolve this syndrome in the ICU.Data were collected from a register of 62 items containing information on the health status of the patient on presenting the syndrome (vital signs, laboratory investigations, etc.), data on the environment, drugs used and other factors that could, a priori, play a role. The statistical analysis was performed using the SPSS program. This prospective study was carried out in a general ICU with ten beds: six beds in an open ward and four individual rooms. Two hundred forty-three patients were admitted during the 6-month study period. The incidence of ICU syndrome was 8.1 % (20 cases). Factors influencing its appearance were the timing of the shifts, the temperature, and whether patients were in individual rooms or open wards. The frequency of the syndrome was much higher in open wards and in the afternoon (from 15:00 to 22:00). In conclusion, the attitude of the nursing staff should be alert to identify the syndrome early and initiate appropriate measures, such as orienting the patient in time and space, achieving an appropriate temperature, using relaxation techniques, facilitating access to the family, etc., since in 35 % of cases these measures are sufficient to stabilize and/or resolve the problem, without the need of drugs.