This is an exploratory, descriptive and qualitative study with the aim of analyzing the knowledge of nurses in an intensive care unit about delirium in critically ill patients. Study participants were fourteen ICU nurses from a public hospital. Data were collected through semi-structured interviews and analyzed using the Collective Subject Discourse technique. Five features were identified after data analysis: signs and symptoms, use of sedatives, physical restraint, environment and lack of professional preparation. It was found that nurses have doubts concerning delirium, its management in intensive care, the use of scales and nursing interventions. This study points to the need for education on the subject and further research on the management of delirium in nursing.