Neuroepidemiology is a discipline assessing the impact of environmental and genetic factors on the incidence and development of diseases of the nervous system and describes their prevalence and distribution. The basic epidemiological parameters in multiple sclerosis (MS) are the indices of prevalence, incidence, morbidity and mortality, disease duration and mean age at onset. First epidemiological studies concerning MS date back to the twenties the XX century. Prevalence indices worldwide vary from 15 to 180 per 100 000 persons; in northern Europe the mean index is 83 per 100 000 and in Poland – 45-92 per 100 000. Incidence indices vary depending on geographic location: in Europe it varies from 3.5 to 5.5 per 100 000, while in Poland they vary from 2.4 (Szczecin) to 4.3 (Gniezno). Based on these data it may be assumed that 1300-2100 new cases are being diagnosed in Poland each year. In females, the prevalence of MS is about two-fold higher than in males. Mean age of onset in the Lublin region is 30.1 years and in the Szczecin region – 36.49 years in males and 34.16 years in females. It is estimated that 10-years’ survival rate (from the time of diagnosis) is 90-95%, 20-years’ survival rate – 70-75%, 30-years’ survival rate – 50-65% and 40-years’ survival rate – 35-55%. Mean life duration in males and in females was similar and in 1998 amounted to 52.3 and 51.8 years, respectively. Patients with late-onset MS usually survive shorter. In 58% of the patients, the disease takes a relapsing-remitting form, in 27% – secondary progressive, in 9% – primary progressive and in 6% – progressive-relapsing. A more severe course may be expected in late-onset cases, in those with high index of relapses in the initial years of the disease and in those with pronounced demyelinating lesions in MRI scans. On the average, disability increases by 0.3-0.5 EDSS grade per year.