MRI lesions disseminated in space:
At least three of the following criteria must be met:

1. One gadolinium-enhancing lesion or nine T2-hyperintense lesions if there is no gadolinium-enhancing lesion
2. At least one infratentorial lesion
3. At least one juxtacortical lesion
4. At least three periventricular lesions

MRI lesions disseminated in time:
At least one criterion must be met:

1. If MRI is more than 3 months after clinical event, then a gadolinium-enhancing lesion at a site different from the original clinical event is sufficient; if there is no gadolinium enhancement, then a follow-up scan is required (usually > 3 months later). A new T2 or gadolinium-enhancing lesion on this second or subsequent MRI fulfills the requirement.
2. If first MRI scan occurs less than 3 months after the onset of the clinical event, then a second scan > 3 months later showing a new gadolinium-enhancing lesion fulfills requirement. If no gadolinium enhancement is seen at this second scan, a further scan not less than 3 months after the first scan that shows a new T2 lesion or an enhancing lesion will suffice.