Introduction: The exposure to shift works, and especially to night shift, goes against the circadian rythmicity of the social man, which brings about a multitude of disruptive effects on health. In a hospital environment, such night shift is necessary so as to ensure the continuity of care. Sleep and vigilance disorders related to this work mode are frequent and often pose adaptation problems. The objective of this study is to detect the harmful effects of night shift on sleep, vigilance and the quality of life of nurses in Farhat Hached Teaching Hospital in Sousse. Material and Methods: It is a cross-sectional study carried out among two groups of nurses: one group performing a fixed night work and the other one working permanently during the day at Farhat Hached Teaching Hospital in Sousse. Data collection is mainly based on validated questionnaires evaluating sleep quality (Pittsburg sleep quality index), daytime sleepiness (Epworth sleepiness scale), sleep typology (Horne and Ostberg questionnaire), and the quality of life (SF-12). An objective evaluation of vigilance was realized by the study of reaction time and error rates to different tasks of "Super lab" software. Results: 50 night and 50 day nurses have been colligated. Both groups were age-and gender-matched. Sleep quality mean index was significantly higher among night nurses in comparison with day nurses (10.2 ± 5.9 versus 6.76 ± 5.16). After multivariate analysis, sleep quality was significantly correlated to age, department, schedule and the choice of schedule. Night shift was not related to daytime sleepiness. The objective analysis of vigilance showed that the reaction time to different tasks exploring the attentional mechanisms, as well as errors rate, were significantly more important among the night group. The mental score of the quality of life was significantly higher among day nurses. However, such difference was not significant with regard to * Corresponding author.W. Boughattas et al. 573physical score. Conclusion: The findings of our study highlight not only the alteration of the health and the well being of paramedical staff secondary to night shift, but also a possible threat to safety care lavished by these teams, which involves the necessity to undertake preventive measures on an individual and collective scale.