The frequency of oligoclonal bands (OCB) restricted to the cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS) varies widely in different populations. The objective of this study was to determine the frequency of these OCB in a group of MS patients in the city of São Paulo. Techniques used to detect OCB consisted of isoelectric focusing followed by immunoblotting. Oligoclonal bands were found in 49 (54.4%) out of 90 patients with clinically definite MS; in (31.2%) of the 16 patients with clinically isolated syndrome; in 7 (17.9%) of 39 patients with inflammatory disorders of the central nervous system (IDCNS), and in none of the individuals with no neurological condition (control group). The specificity of the method was 100% when compared to the control group and 82.1% when compared to the IDCNS group. These results suggest that the frequency of CSF OCB is much lower in Brazilian MS patients from São Paulo city than that reported in MS series from Caucasian populations.