Hidden hypercortisolism (HidHyCo), a condition of cortisol excess in the absence of its classical signs and symptoms, isassociated with an increased risk of osteoporosis and fragility fractures, which are a significant cause of morbidity, mortalityand health care costs.The HidHyCo screening in populations at risk is a matter of debate: the HidHyCo case finding is of utmost importance sincethe resolution of cortisol excess can result in the improvement of bone strength and in the reduction of fracture risk.The aim of the current project is the assessment of the prevalence of HidHyCo and of the characteristics predictive of thepresence of this condition in patients with apparently primary osteoporosis. Moreover, this project was aimed at evaluatingthe pathogenetic mechanisms explaining the negative effects of this slight cortisol excess on bone and the potential role ofthe genetic background and of the gut microbiome