OBJECTIVE: The aim of the study was to evaluate whether myo-inositol (MI) treatment during semen preparation procedures is able to improve fertilization rate (FR) and embryo quality (EQ) after ICSI. DESIGN: The study was designed as a prospective randomized single blind controlled trial on sibling-oocyte and was performed from March to December 2013 (NCT02050672). Before recruiting, the sample size was calculated via a power analysis and the FR was designed as primary outcome. In particular, based on a difference of 15% on the FR, and power of 90% and confidence of 95%, a minimum of 210 oocytes per group were required. MATERIALS AND METHODS: Inclusion criteria: 1)couple counseled for ICSI due to male factor; 2) fresh cycles 3) men with ejaculated spermatozoa; 3) women age of >35 yrs; 4) R2 MII oocyte retrieved. At ovum pick up, oocytes were randomly divided in two groups. Mature oocytes of one group (MI) were injected with spermatozoa prepared with routinely used media enriched with 2mg/ml of MI (Andrositol LAB Lo.Li. Pharma), mature oocytes of the other group (CTR) were injected with spermatozoa prepared with routinely used media. Secondary outcome was the EQ. A blinded embryologist performed ICSI procedure and embryo evaluation. RESULTS: In summary, FR cleavage rate (CR) and EQ were significantly higher in MI group. Furthermore, significantly more embryos of the MI group were transferred at day 3; noteworthy, the blind researcher has chosen to transfer only embryos belonging to the MI group with a significant higher frequency.