In intensive care units (ICU), patients in life-threatening situations are hospitalized. While the health status of these patients is often severely compromised, therapeutic interventions include endo-tracheal intubation with artificial ventilation, sedation, and analgesia which restrict their ability to communicate. These patients become additional vulnerable since their pains may not been adequately identified. Uncontrolled pain in sedated and artificial ventilated patients lead to increased number of respiration days and increased length of stay in hospital, which, may result in increased morbidity. This situation appears precarious since pain assessment of these patients in daily clinical practice seems often based on subjective criteria by the health care staff in charge. The purpose of this study was to describe pain-assessment instruments for sedated and artificial ventilated ICU-patients in view of validity, reliability and clinical application. With a systematic literature review, a total of 61 articles were identified in the databases of PUB-MED (National Library of Medicine) and CINAHL (Cumulative Index to Nursing and Allied Health Literature ) and additional bibliographic sources. Indicators for pain in sedated and artificial ventilated ICU-patients were physiological and behavior-related, without biochemical parameters. In most of the instruments, the validity was tested only superficially and no detailed reports regarding the application in everyday practice were given. However, the studied instruments includes algorithm as a significant component which enable decision making of the health care providers in order to execute stepwise pain management interventions. In conclusion, a need for further research to disclose pain indicators in sedated and artificial ventilated ICU-patients, continuous development of instruments and their validation in clinical practice is obvious.