Objective: to assess whether shift work has a cause-effect nexus with the Incidence of metabolic syndrome. Design: retrospective follow-up study, case-control type. Research Methods and Procedures: a total of 202 female and male nurses, aged 23-60 years, having a 1 year minimal follow-up, and without any metabolic syndrome criterion at the first visit were evaluated. The ATP modified criteria were applied for the diagnosis of metabolic syndrome. Moreover smoking habitus, alcohol consumption, educational level and physical activity were considered as bias factors. The.sample was divided in two groups doing or not night shifts. Results: the metabolic syndrome incidence resulted significantly greater in shift workers than in other workers (OR: 4.10, 95% C1 1.34-12.55. p=0.01). The difference was more evident in subjects aged <40 years (OR=6.6, 95% C1 1.05-40.85, p=0.04) the different metabolic syndrome incidence between two groups was detectable even after the multivariate analyse, which considered all the bias factors evaluated. Conclusions: this study shows for the first time that the night shift work is associated with a greater risk to develop metabolic syndrome in workers healthy in baseline conditions.