Recent studies have shown the relevance of the cerebral grey matter involvement in multiple sclerosis (MS). Cortical lesions (CLs), detected by specific MRI sequences, are likely to become a new research outcome in MS studies. The aim of this study was to infer the optimal statistical model describing the distribution of CLs in patients with relapsing-remitting (RR)MS. The negative binomial model gave the best fit to the observed distribution of CLs in a group of 44 RRMS patients with one MRI scan of the brain. This observation has important implications for the statistical analysis of CLs in MS studies.