There are some tests that can be taken to find out if you have MS.

MRI - An MRI is Magnetic Resonance
Imaging. It is a test that produces a
picture of your brain. It allows the
doctor to see if there are any "plaques"
or other abnormalties.
The person just lies down on a table
that moves inside the machine which is
tube shaped, and a magnet sends the
information to a computer which in turn
makes the
images.
CSF - The cerebrospinal fluid surrounds
the brain and spinal cord and some parts
within the nervous system. A needle can
be inserted into the lower back to
remove some of this fluid. The fluid is
then examined.
There are a few other tests that the doctor may decide to take. It is your doctors decision as to what tests he/she needs the person to undergo so he/she can make a diagnosis.