Abstract Background Gestational diabetes mellitus (GDM) is defined as glucose intolerance with onset during pregnancy. It is characterized by high risk of adverse outcomes for the mother and the foetus, if not adequately controlled. The aim of the study was to evaluate the effects of 4000 mg of myoinositol supplementation in women with GDM on maternal-foetal outcomes, compared to controls. Methods A cohort of 330 women with GDM, 150 supplemented with myoinositol and 180 controls were enrolled. Clinical and metabolic parameters and the prevalence of maternal and foetal complications were assessed. Results The same number of women in the two groups started insulin as additional therapy. Women treated with myoinositol more frequently had a long-acting insulin scheme of treatment than those untreated (p