Multiple sclerosis (MS) affects all aspects of a person's life. Considering the unpredictable progress of MS, Patients suffer from uncertainty about their future health and wellbeing which causes psychological distress and social degradation and consequently it affects the development of the disease. This study aims to investigate the relationship between uncertainty in the disease with the frequency of hospitalization in patients with multiple sclerosis who referred to the Zanjan MS Society. This descriptive-correlation research was conducted in Zanjan MS Society in 1395. A total of 100 patients with MS were selected randomly without placement. The data gathering tool that is used is a demographic questionnaire and Mishel Uncertainty in Illness Scale (MUIS-C) questionnaire. Data were analyzed by SPSS version 16 at a significant level less than 0.05. The results have shown that in this research there was a significant positive correlation between uncertainty and frequency of recurrence (r = 0.387 p = 0.002) and hospitalization (r = 0.261 p = 0.013) during 1 year and people with more uncertainty experienced more recurrence and hospitalization. This study shows that uncertainty in the disease affects the frequency of relapse and admission of MS patients. It seems that finding a way to control the amount of uncertainty in the disease can control the tensions caused by uncertainty in the disease and, consequently, the progression of the disease.