In the present study we report, as part of a large multiple sclerosis (MS) cohort (1800 patients), three cases of untreated patients who developed autoimmune hepatitis (AIH). The prevalence of AIH in the general population is about 0.0169% and seems to be higher in our MS cohort (0.17%). We suggest that a liver biopsy should systematically be performed in untreated MS patients with a sustained increase of liver enzyme.