The objective of the study was to evaluate whether the presence of oligoclonal bands (OB) adds information in predicting CIS conversion to clinical definite multiple sclerosis (CDMS) and conversion time to CDMS. From 1998 to 2006, CIS patients were included in a prospective study. Patients underwent brain MRI and OB determination within 2 months of the first demyelinating event. We analyzed conversion to CDMS and time to conversion to CDMS according to abnormal MRI and the presence of OB. Forty patients were included. Fifteen patients (37%) converted to CDMS; 14 of them (93.3%) had abnormal baseline MRI (P = 0.01, RR = 5.9; 95% CI 1.3-10.1) and 13 (86.7%) had positive OB in CSF (P = <0.01, RR = 5.3; 95% CI 1.6-9.5). The risk of conversion to CDMS in patients with positive OB and abnormal baseline MRI was significantly higher compared to patients negative for both tests or with only one positive (RR = 9.1; 95% CI 3.5-14.6). Time to conversion to CDMS was 6.8 +/- 3.5 months for patients with OB and abnormal baseline MRI and 19 +/- 14 months for patients with only one abnormal test. CIS patients with abnormal baseline OB in CSF have a higher risk for developing CDMS. Regarding conversion time to CDMS, when abnormal MRI was added to positive OB, patients converted faster (mean time, 6 vs. 19 months). This information may be useful when considering treatment in CIS patients.