Background. Clinically isolated syndrome (CIS) is the first neurologic episode of multiple sclerosis (MS). Magnetic resonance imaging (MRI) and clinical features are used to predict risk of conversion to MS. Objectives. The aim of this prospective study is to evaluate predictors of conversion of CIS to McDonald MS. Method. 97 patients with CIS have been followed for 2 years. Age of onset, gender, initial clinical presentation, and MRI brain and spine were assessed. The 2010 revised McDonald criteria were applied. Results. Fifty-nine patients (60.8%) with CIS converted to McDonald MS after 10.1 + 4.2 months. Thirty-seven (38.1%) of the convertors satisfied the diagnostic criteria based on the radiological parameters, while 21.7% sustained their second clinical events. A multivariate regression analysis revealed that high number of lesions in MRI (P = 0.001) and earlier age of onset (P = 0.043) predicted the conversion of CIS to McDonald MS. Gender (P = 0.5) and initial clinical presentation (optic pathway (P = 0.4), supratentorial (P = 0.91), brain stem/ cerebellum (P = 0.97), and spinal (P = 0.76)) were not statistically significant. Conclusion. Age of onset and MRI parameters can be used as predictors of CIS conversion to McDonald MS. Application of the 2010 revised McDonald criteria allows an earlier MS diagnosis.