BACKGROUND It is recognized that there is a particular geographic and ethnic distribution of neuromyelitis optica (NMO) among Caucasian and non-Caucasian populations. OBJECTIVE To review the diagnoses of patients whom were enrolled in the South Atlantic Project, a Brazilian multiple sclerosis (MS) survey performed from 1995-1998, and to identify NMO and MS case frequencies. METHODS We reviewed the data from a 10-year follow-up of MS patients. To apply the current diagnostic criteria, the neurologists were asked to collect clinical and laboratory data from the medical records of study patients treated from 1999-2009. RESULTS The spectrum of inflammatory demyelinating disease in 322 patients (67% white; 33% African-Brazilian) was: 49 (15%) with NMO; 14 (4%) with NMO syndromes; 10 (3%) with acute disseminated encephalomyelitis (ADEM); one isolated tumefactive brain lesion; 249 (77%) with MS (151 with relapsing-remitting MS (RRMS), 70 with secondary progressive MS (SPMS) and 27 with primary progressive MS (PPMS)). Disability was more severe in NMO and PPMS. One-third of the NMO patients had died. CONCLUSIONS The frequency of NMO was 6.8% in São Paulo and 20.5% in Rio de Janeiro, and mainly seen in persons of African descent, which strengthens the hypothesis of there being an ethnic association of this disease. We recommend that epidemiological studies on MS that were performed previously be reviewed again, to ensure more accurate diagnoses.