Intensive Care Unit (ICU) is an autonomous section which requires the cooperation of skilled health professionals and the use of advanced technology to provide intensive care in severely ill patients. The ICU nurse must be possessed of specialized clinical knowledge and experience to be able to respond effectively to their role, which appears to be adequately investigated in our country. Purpose: The investigation of the real and functional role of nurses working in ICU, on the interventions they perform. Material-Method: As for the design, it was a cross-sectional study. The studied population consisted of 222 registered nurses (response rate 74%) working in ICU, of 12 hospitals in Athens. For data collection, which lasted 5 months, it was used a special designed questionnaire. It was investigated the frequency of carrying out various nursing interventions and their relation to various socio-demographic characteristics of the nursing staff. Data analysis was performed with the statistical package STATA ™, ver.9. Results: Of the 222 registered nurses, 80% were women. The average age of nurses was 34.16 (± 6.41) years, while the average years of work in the ICU was 8.52 (± 6.19) years. Regarding the education level of respondents 20.7% was university graduates and 79.3% was technological institute graduate. Although the ICU nurses perform a series of interventions with significant variation in their frequency, however, appear to be characterized by low autonomy, since interventions without medical advice or in emergency situation is made by a small proportion of staff. The implementation of these interventions was not associated statistically significantly with age, sex, education level and years of nurse's work. The exceptions were the measurement of central venous pressure (p<0,001) and the use of external pacemaker (p = 0,002), actions most frequently performed by nurses with more years of experience in the ICU and of university education. Conclusions: The Greeks ICU nurses are characterized by low autonomy in carrying out interventions without a medical directive or in emergency situations. This autonomy was not associated with factors such as age, sex, clinical experience and level of training of nurses, in contrast to the literature. Characteristics of the Greek reality, as the problematic organization of hospitals, lack of cooperation, the shortage of nurses in clinical training, the reduced nursing staff, the increased workloads and low satisfaction with the profession could explain the findings of this study.