Purpose To investigate the value of proprotein-converting subtilisin kexin type 9 (PCSK9) levels in type 2 diabetes mellitus (T2D) patients with different stages of diabetic retinopathy (DR) and to compare these findings with a healthy control group without diabetes mellitus (DM). Methods A total of 135 patients, 100 of whom were patients with T2D and 35 of whom were in the health control group, were included in this prospective study. T2D patients were divided into three groups: the first group included 34 people with T2D without DR, the second group had 32 people with non-proliferative DR (NPDR), and the third group had 34 people with proliferative DR (PDR). Serum PCSK9 levels were analyzed and compared between the groups. Results Forty-nine percent of the participants were female, and the mean age was 64 ± 9.1 years, with no statistically significant results between the four groups in terms of age and sex. The mean serum PCSK9 value was significantly different (p = 0.01) when all groups were evaluated, and statistically significant change was observed with the progression of DR. When serum PCSK9 levels were evaluated in all T2D patients (groups 1, 2, and 3), a medium-level correlation was observed with low-density lipoprotein (p < 0.05). Conclusion Serum PCSK9 values differed significantly in diabetic patients compared to the control group. One should be clinically cautious about the usefulness of circulating PCSK9 concentrations as an indicator of the risk of diabetic retinopathy.