The prevalence of probable multiple sclerosis (MS) in Caltanissetta city, Sicily, is at least 51 per 100,000. If possible multiple sclerosis patients are included, it is 54 per 100,000. This value is similar to that found in other cities in Sicily: Enna, Monreale and Agrigento. The high prevalence of multiple sclerosis in Caltanissetta confirms the previous data on Sicily and emphasises the importance of small population studies in the epidemiology of MS.