The radiologically isolated syndrome (RIS) was defined in 2009 as the presence of asymptomatic, incidentally identified demyelinating-appearing white matter lesions in the central nervous system within individuals lacking symptoms typical of multiple sclerosis. The RIS criteria have been validated and predict the transition to symptomatic MS reliably. The performance of RIS criteria that require fewer MRI lesions is unknown. 2009-RIS subjects, by definition, fulfill 3-4 of 4 criteria for 2005 dissemination in space [DIS] and subjects fulfilling only 1 or 2 lesions in at least one 2017 DIS location were identified within 37 prospective databases. Univariate and multivariate Cox regression models were used to identify predictors of a first clinical event. Performances of different groups were calculated. 747 subjects (72.2% female, mean age 37.7 ± 12.3 years at the index MRI) were included. The mean clinical follow-up time was 46.8 ± 45.4 months. All subjects had focal T2 hyperintensities suggestive of inflammatory demyelination on MRI; 251 (33.6%) fulfilled 1 or 2 2017 DIS criteria (designated as Group 1 and Group 2, respectively), and 496 (66.4%) fulfilled 3 or 4 2005 DIS criteria representing 2009-RIS subjects. Group 1 and 2 subjects were younger than the 2009-RIS Group and were more likely to develop new T2 lesions over time (p < 0.001). Groups 1 and 2 were similar regarding survival distribution and risk factors for transition to multiple sclerosis. At five years, the cumulative probability for a clinical event was 29.0% for Groups 1-2 compared to 38.7% for 2009-RIS (p = 0.0241). The presence of spinal cord lesions on the index scan and CSF-restricted oligoclonal bands in Groups 1-2 increased the risk of symptomatic MS evolution at five years to 38%, comparable to the risk of development in the 2009-RIS group. The presence of new T2 or gadolinium-enhancing lesions on follow-up scans independently increased the risk of presenting with a clinical event (p < 0.001). The 2009-RIS subjects or Group 1-2 with at least 2 of the risk factors for a clinical event demonstrated better sensitivity (86.0%), negative predictive value (73.1%), accuracy (59.8%) and area under the curve (60.7%) compared to other criteria studied. This large prospective cohort brings Class I evidence that subjects with fewer lesions than required in the 2009 RIS criteria evolve directly to a first clinical event at a similar rate when additional risk factors are present. Our results provide a rationale for revisions to existing RIS diagnostic criteria.< Réduire