Background: Multiple sclerosis (M.S) is the most common cause of neurological disability in young adults but its etiology is still unknown. It occurs due to a combination of both genetic and environmental factors. The objective was to determine the prevalence of M.S in the northern cities of Khuzestan (Iran) and its relation to familial history, smoking, the month of onset, stress, and immigration. Patient and methods: This study is a one-step descriptive correlation analysis. Data were collected through a questionnaire completed in a face to face conversation setting and further analyzed using SPSS 17 software package. Statistical significance was determined by chi-square test (p<0.05). Results: The sample size in this study was 142. Prevalence of M.S in the north of Khuzestan in Iran were 15 per 100,000 people. 11% of patients had a positive familial history of M.S. There was a statistically significant correlation between sex and positive family history (p=0/03) and it was higher in men. Familial MS was higher in siblings than parents or children. 93% of patients were non-smoker, beginning of disease in 37.2% of cases was in summer and 70% of patients had no history of immigration. In 68% of patients, the onset of M.S. co-occurs with stress and there was a statistically significant relationship between stress and symptoms at onset. Conclusion: In recent years, increasing rate of M.S. was observed. The incidence of M.S in men with positive familial history was higher than in women; paternal positive history was four times higher than maternal ones. Further studies are needed to clarify the underlying genetic or environmental factors that explain this association. Extensive research is also required to investigate the possibility of a relationship between stress and disease
