Objective To investigate the relationship of carotid plaques with platelet-to-lymphocyte ratio (PLR) and neutrophil-to-lymphocyte ratio (NLR) in young patients newly diagnosed with type 2 diabetes mellitus (T2DM).Methods The medical record data were collected from young patients newly diagnosed with T2DM and carotid atherosclerosis (268 cases, observation group); the patients were divided into intima-media thickening (IMT) group (116 cases) and plaque group (152 cases) according to the intima-media thickness; the plaque group was subdivided into grade I plaque group (62 cases), grade Ⅱ plaque group (47 cases), and grade Ⅲ plaque group (43 cases) using a semi-quantitative method; additionally, 104 young people with normal carotid intima thickness as determined by concurrent physical examinations were enrolled as control group. The relationship of carotid plaques with PLR and NLR was analyzed, and the role of PLR and NLR in the diagnosis of patients with carotid atherosclerosis was evaluated.Results The PLR and NLR in the observation group were significantly higher than those in the control group (P<0.05); the two indices in the plaque group were significantly higher than those in the IMT group (P<0.05); the two indices in the grade Ⅲ plaque group were significantly higher than those in the grade Ⅱ and grade I plaque groups (both P<0.05); the two indices in the grade Ⅱ plaque group were significantly higher than those in the grade I plaque group (P<0.05). The PLR and NLR values of patients in the plaque group were positively correlated with the grade of plaques (r=0.687, P<0.05). The area under the ROC curve for predicating carotid atherosclerosis using the PLR was 0.722 (95% confidence interval [CI]: 0.663~0.790) with the corresponding cut-off value, sensitivity, and specificity being 111.086, 0.789, and 0.612, respectively. The area under the ROC curve for predicating carotid atherosclerosis using the NLR was 0.653 (95%CI: 0.586~0.723) with the corresponding cut-off value, sensitivity, and specificity being 2.240, 0.809, and 0.511, respectively.Conclusions The PLR and NLR may be related to carotid endothelial inflammation in patients newly diagnosed with T2DM and are positively correlated with carotid plaque scores; thus, it is possible, to some degree, to predict the degree of carotid atherosclerosis in patients newly diagnosed with T2DM using the above two indices.