- To evaluate the cognitive status (attention/concentration) and the influence of cognitive impairment on QoL in subjects with RRMS during two years of treatment with RNF Subjects will be treated according to widely-acknowledged standards for MS treatment and the choice of drug will depend solely on medical indications. The potential subjects will have been prescribed Rebif for the first time by their treating physicians and will then be given the option to enter in this observational study. As this is purely an observational study, the subjects will be followed by their treating physicians, according to current medical practice and Rebif SmPC (Summary of Product Characteristics) requirements (i.e monitoring of thyroid and liver enzymes prior to the start of therapy, and hepatic function at months 1, 3, 6 and periodically thereafter, prescription of antipyretics etc.) After each control visit, the treating physician will complete subject's observations chart. The planned schedule of visits will be identical to the routine schedule of control visits dictated by the National Health Found: 1st Visit - 3 months after RNF therapy start, 2nd Visit - after 6 months, 3rd Visit - after 9 months, 4th Visit - after 12 months, 5th Visit - after 18 months, 6th Visit - after 24 months.