The importance of MRI stuides in the control over treatment efficacy in multiple sclerosis and appropriate recommendations on drug substitution during treatment are discussed. We suggest low, middle or high risk in respect to the efficacy of current treatment. Accordingly, drug substitution can be related with the low level of fears for all three criteria or the moderate level for any two criteria or the high level for any one criterion. Since MRI criteria are important, this model appears to be the most rational because the physician can make a decision about treatment escalation if the patient has ≥3 new T2-lesions or ≥3 contrast-enhanced T1-lesions.