"Asymptomatic multiple sclerosis (MS)" or "subclinical MS" describes "a clinically silent disease state of MS" discovered by chance either by imaging or at autopsy, or with incidental findings shown by other diagnostic tools that are consistent or suggestive of MS, and that cannot be explained by any other disease or condition. Since the early 1960s there have been a number of autopsy studies reporting cases, in which histopathological brain changes consistent with MS were found, despite that none had any clinical symptom or sign of the disease during their lifetime. Several reports have also shown that asymptomatic first-degree relatives of MS patients may have oligoclonal bands in their cerebrospinal fluids or may turn out to have abnormal evoked potential studies. With the extensive availability of MRI lately, the incidence of individuals having these studies performed for indications other than suspicion of inflammatory demyelinating disease of the central nervous system (CNS) such as primary headaches or trauma, revealing unsuspected brain and/or spinal cord lesions compatible with MS had raised. A number of such case-series reported recently had resulted in increased awareness of this finding and to its relationship to clinical multiple sclerosis. This situation is now referred as "radiologically isolated syndrome (RIS)" and is the most common type of "asymptomatic MS". Since it is well known that MS has an asymptomatic period of unknown duration in many individuals preceding its initial presentation, either as a clinically isolated syndrome or in rare instances as primary progressive-MS, it is likely that a number of MS patients will be diagnosed by chance as RIS at an early stage before converting to clinical disease. Currently this issue has gained a wide interest as there are no established protocols regarding how to study and follow these individuals or whether they should be treated or not! However, not all patients with RIS are predestined to develop clinical disease and it was recently shown that the rate of conversion to clinical MS is about one-third of RIS cases at five years. Although that there may be some risk factors suggestive of a higher or earlier conversion to clinical disease, none are definite and the current evidence is not supportive of initiating treatment in patients diagnosed as RIS.