The purpose of this study is to determine if sexual dysfunction symptoms and quality of life measures in patients with Multiple Sclerosis may be improved in patients that are prescribed Tysabri.

Patients will be naive to Tysabri at the baseline for this study then their sexual dysfunction, fatigue, and quality of life measures will be measured using scaled questionnaires.

Inclusion Criteria:

1. Must give written informed consent and provide all authorizations required by local law(ex. Protected Health Information, PHI)
2. Minimum baseline score of 15 for the primary sexual dysfunction subscale of the MSISQ-19 (questions 12,16,17,18,19)
3. Men and Women between 18 and 60 years of age
4. Must have EDSS less than or equal to 5.5 at baseline
5. Must be able to walk at least 100m without assistive devices
6. Must have a documented diagnosis of a relapsing remitting form of MS as defined by the revised McDonald Committee criteria (Polman et al.,2005)
7. Must have a recent MRI (within 1 year from baseline)
8. Must satisfy the locally approved therapeutic indications for TYSABRI
9. Must be stable in disability for at least 30 days prior to enrollment to the study
10. Must be Natalizumab naïve
11. Must be stable in symptomatic management of the disease, for at least 30 days prior to enrollment in the study
12. Must be on a stable regimen of all symptomatic medications for Multiple Sclerosis especially those that could interfere with sexual function (specifically anti-cholinergics, anti-hypertensives, etc.) for at least 30 days prior to the enrollment.
13. Must be considered by the Investigator to be free of signs and symptoms suggestive of PML based on medical history, physical examination, or laboratory testing.
14. Must be willing to discontinue and remain free from concomitant immunosuppressive or immunomodulatory treatment (including IFN and GA) while being treated with Natalizumab during the study

Exclusion Criteria:

1. Must give written informed consent and provide all authorizations required by local law(ex. Protected Health Information, PHI)
2. Minimum baseline score of 15 for the primary sexual dysfunction subscale of the MSISQ-19 (questions 12,16,17,18,19)
3. Men and Women between 18 and 60 years of age
4. Must have EDSS less than or equal to 5.5 at baseline
5. Must be able to walk at least 100m without assistive devices
6. Must have a documented diagnosis of a relapsing remitting form of MS as defined by the revised McDonald Committee criteria (Polman et al.,2005)
7. Must have a recent MRI (within 1 year from baseline)
8. Must satisfy the locally approved therapeutic indications for TYSABRI
9. Must be stable in disability for at least 30 days prior to enrollment to the study
10. Must be Natalizumab naïve
11. Must be stable in symptomatic management of the disease, for at least 30 days prior to enrollment in the study
12. Must be on a stable regimen of all symptomatic medications for Multiple Sclerosis especially those that could interfere with sexual function (specifically anti-cholinergics, anti-hypertensives, etc.) for at least 30 days prior to the enrollment.
13. Must be considered by the Investigator to be free of signs and symptoms suggestive of PML based on medical history, physical examination, or laboratory testing.
14. Must be willing to discontinue and remain free from concomitant immunosuppressive or immunomodulatory treatment (including IFN and GA) while being treated with Natalizumab during the study

From signing of the consent to last visit (month 6)