Background <p>There is an increased risk of diabetes and cardiovascular disease among patients with psoriasis. However, whether diabetes affects the cardiovascular adverse events in patients with psoriasis who have suffered from coronary artery disease remains unclear. This study aimed to explore the prognostic role of diabetes in this particular population.</p> Methods <p>This single-center, retrospective cohort study included all consecutive adult patients with psoriasis and coronary artery disease admitted at our hospital between January 2017 and May 2022. Clinical records were collected and compared between patients with and without diabetes. Survival curves were derived using Kaplan–Meier methods. Multivariable Cox regression was used to control potential confounding.</p> Results <p>This study included 305 participants, including 147 patients (48.2%) with diabetes. Patients with diabetes were more likely to have hypertension (<i>p</i> = 0.045), peripheral vascular disease (<i>p</i> = 0.043) and the history of stroke (<i>p</i> = 0.041). Patients with diabetes also had higher levels of low-density lipoprotein cholesterol (<i>p</i> = 0.039) and homocysteine (<i>p</i> = 0.006). After a median follow-up of 36 months, patients with diabetes had a higher incidence of major adverse cardiovascular events (MACE) than patients without diabetes (<i>p</i> = 0.032). According to the results of the Cox regression analysis, only diabetes (<i>p</i> = 0.039) was associated with MACE. The subgroup analysis showed that diabetes was associated with MACE, especially in male patients (<i>p</i> = 0.008) and those without chronic kidney disease (<i>p</i> = 0.021).</p> Conclusion <p>In patients with psoriasis and coronary artery disease, diabetes is independently linked with MACE. These findings will help the risk assessment for patients with psoriasis and coronary artery disease.</p>