Background: Erectile dysfunction (ED) is prevalent, especially in diabetes mellitus, and may represent a vascular disorder. Penile Doppler ultrasound has emerged as a means of assessing penile blood flow, but the relationship with ultrasound and blood glucose is yet to be determined. Objective: To systematically evaluate the role of penile Doppler ultrasound in assessing vascular abnormalities in erectile dysfunction patients and its association with glycemic control. Methods: A systematic review on PRISMA 2020 was conducted. The search strategy was electronic databases ‘PubMed, Scopus, Web of Science and Google Scholar’ from 2020 to December 2025. The studies that provided measurements of penile Doppler (peak systolic velocity [PSV], end diastolic velocity [EDV] and resistive index [RI]) in men with erectile dysfunction (ED) were considered. Those that reported information regarding insulin resistance (HbA1c), duration of diabetes and erectile function were included. A narrative approach was taken due to the variability of data. Results: A total of 9 studies were included. The majority of studies showed decreased PSV and increased EDV, suggestive of arterial inflow and venous leak. Poorer blood glucose control (higher HbA1c) was generally associated with abnormal penile blood flow, with decreased PSV, increased EDV and decreased RI. Other studies demonstrated that longer duration of the disease was associated with worse erectile dysfunction and Doppler results. Fibrosis was noted in some studies. Conclusion: Penile color Doppler ultrasound is a reliable diagnostic tool for evaluating vascular causes of erectile dysfunction. Poor glycemic control is strongly associated with impaired penile hemodynamics, emphasizing the importance of integrated metabolic and vascular assessment in ED patients.