Patients with clinically isolated syndrome (CIS) by definition do not have multiple sclerosis (MS) but are at risk of developing it. While studies show earlier immunomodulating drug use is effective, treatment must consider likely patient prognosis. In this paper we review current diagnosis, prognosis, and treatment literature for patients with CIS within Latin American clinical settings. Latin American MS experts, convened by ACINDES (The Civil Association for Research and Development in Health), reviewed current CIS (and early MS) literature and drew consensus conclusions. Three subgroups addressed separate questionnaires on CIS issues: prognosis, diagnosis, and treatment. MRI can contribute to predicting MS risk in patients with CIS; in Latin America, investigation of haplotype presence associated with CIS would be appropriate. McDonald's criteria and subsequent revisions enable earlier, more accurate MS diagnosis. Type A evidence exists supporting all leading immunomodulating MS drugs for effective treatment of CIS with a high risk of conversion to MS. In conclusion, patients with CIS are usually young, with often-limited symptomatic manifestations, and must be adequately prepared to receive preventive treatment. This consensus review should contribute to the dialogue between physicians and patients.