Objective: To determine whether a low glycemic index diet is better than a normal glycemic index diet in producing ovulatory cycles in women with polycystic ovary syndrome (PCOS) and anovulation. Materials and Methods: A randomized controlled clinical trial involving 37 women with PCOS and anovulation. The authors randomly assigned low glycemic index diets (n = 19) and normal glycemic index (n = 18) diets, and analyzed the number of ovulatory cycles for three months. Results: In patients who consumed a low glycemic index diet, 24.6% (14/57) of the cycles were ovulatory. In those who consumed a normal glycemic index diet, only 7.4% (4/54) of the cycles were ovulatory (p = 0.014). Conclusions: The difference observed in the number of ovulatory cycles could be related to a decrease in the serum levels of circulating androgens, secondary to an improvement in insulin resistance.