: This Experts’ opinion aims to offer an updated scientific support for the therapeutic use of Inositols in Polycystic Ovary Syndrome (PCOS) and non-insulin dependent (type 2) diabetes mellitus (NIDDM), providing a practical support for gynecologists, obstetricians, endocrinologists, nutritionists, developmental and system biologists, neurologists and general practitioners.: This paper summarizes the physiology of Myo-Inositol (MI) and D-Chiro-Inositol (DCI) and their therapeutic role, also for fertilization. The document highlights some deep differences between the physiological functions of MI and DCI, taking also in consideration the safety and intestinal absorption. Updates include new evidence on the efficacy exerted in PCOS by the 40:1 MI/DCI ratio, as well as the innovative approach based on alpha-lactalbumin to overcome the therapeutic decreased efficacy of Inositols in some patients.: The available evidence suggests that MI, alone or in combination with DCI in the 40:1 ratio, offers a promising treatment for PCOS and NIDDM. However, additional studies need to evaluate some still unresolved issues, such as the best MI/DCI ratio for treating NIDDM, the potential cost-effectiveness of reduced gonadotropins administration in IVF due to MI treatment, or the benefit of MI supplementation in ovulation induction with clomiphene citrate in PCOS patients.