Radiologically isolated syndrome (RIS) is the earliest stage in the disease continuum of multiple sclerosis (MS). RIS is discovered incidentally in individuals who are asymptomatic but have typical lesions in the brain and/or spinal cord suggestive of demyelination. The 2009 and revised 2023 RIS criteria were developed for diagnosis. Presymptomatic individuals who fulfill the 2009 RIS criteria by having 3-4 of 4 dissemination in space McDonald 2005 MS criteria are still diagnosed with RIS using the revised 2023 RIS criteria. In presymptomatic individuals who do not fulfill the 2009 RIS criteria, the revised 2023 RIS criteria target to secure an accurate and timely diagnosis: In addition to (a) having one lesion in two of four locations (periventricular, juxtacortical/cortical, infratentorial, spinal cord), (b) two of three features (spinal cord lesion, cerebrospinal fluid (CSF)-restricted oligoclonal bands, and new T2 or gadolinium-enhancing lesion) should be fulfilled. Among laboratory biomarkers, CSF kappa-free light chain can also increase diagnostic accuracy. Once the diagnosis is confirmed, the established risk factors, including demographics, imaging, and laboratory biomarkers, should be evaluated for symptomatic MS transition and prognosis. Younger age, male sex, increased neurofilament-light chain, CSF abnormality, and the presence of infratentorial, spinal cord, or gadolinium-enhancing lesions on imaging are the main risk factors for transition to symptomatic MS. Two randomized clinical trials showed significant efficacy of disease-modifying treatments in delaying or preventing the development of the first clinical event in RIS. However, because some individuals remain as RIS, it is crucial to identify the individuals with a higher number of risk factors to optimize disease outcomes by early intervention while minimizing adverse events. Discussing each RIS case with an expert MS team is recommended because there is still a lack of clinical guidelines to improve care, counseling, and surveillance.