Only a few studies have investigated the association between the severity of Peyronie disease (PD) and clinical parameters such as age and associated comorbidities. The aim of this study was to report the relationship between the degree of curvature of the penis and the clinical parameters among patients with PD. A total of 1001 patients with PD were evaluated retrospectively in terms of penile deformity, erectile status, and risk factors for systemic vascular diseases. The degree of curvature was assessed with a protractor during maximum erection in response to a combined injection and stimulation test and/or vacuum device. A modified Kelami classification was used to categorize penile deformities as follows: patients with deformities without curvature (notching, hourglass, and swan neck deformity, group 1), with mild curvature (<= 30 degrees, group 2), with moderate curvature (31-60 degrees, group 3), or with severe curvature (>60 degrees, group 4). Chi-square tests, 1-way analysis of variance, and univariate and multiple ordinal regression analyses were used for statistical analysis. Penile deformity without curvature was detected in 12.3% of the patients, whereas the curvature was less than 30 degrees in 39.5%, 30 to 60 degrees in 34.5%, and more than 60 degrees in 13.5% of the patients. Multiple ordinal regression analysis identified age (P = .013), side of deformity (P = .007), erectile dysfunction (P < .0001), and diabetes mellitus (P = .001) as significant independent predictors of the severity of penile curvature. In conclusion, patients' age, side of deformity, erectile function, and diabetes were significantly associated with the degree of curvature.