Objective: The aim of this case-control study was to investigate the association between Dietary Inflammatory Index (DII) and PCOS risk in the 120 newly-diagnosed cases of PCOS and 120 healthy controls aged between 18-45 years in Khorramabad of Iran. Results: Energy intake was significantly more in PCOS patients (p=0.01) and these people were less active than control women (p=0.001). The mean ± SD of DII in PCOS patients was 0.4±2.09 while it was 0.45±1.92 in control group (p=0.001). There was a positive association between increasing DII score and the risk of PCOS with the OR of 2.41(1.15, 5.02) in the crude model when we compared the fourth quartile with the lowest one. This association was still significant in several models after adjusting for age and energy intake in the model 1 (P- value for trend=0.001), in the second model and after adjusting for the level of activity, education, and family history of PCOS along with the first model (P- value for trend 0.003), and finally after additional adjustment for BMI in model 3 (P- value for trend 0.003). Results of present study showed that consuming more pro-inflammatory diets with higher DII scores are associated with increased risk of PCOS.