We present the results of an epidemiological survey on MS conducted in the provinces of Reggio Emilia and Modena (4,980 km2) from 1970 to 1990. The population increased from 943,182 residents in 1970 to 1,024,223 in 1990, with an average population during the period of the survey of 993,056. The mean annual incidence was 1.59 cases/100,000 inhabitants (c.i. 95% 1.42-1.78). The prevalence as of December 31, 1990, was 39.44/100,000 inhabitants. Our study is a further demonstration that Italy is a high-risk zone for this disease, and also demonstrates the possibility of carrying out reliable epidemiological surveys even over extensive territories.