BACKGROUND: There is increasing recognition Functional Neurological disorder (FND) is comorbid with other neurological conditions, but little is known about patients with Multiple Sclerosis (MS). We therefore systematically evaluated the presence of FND in consecutive patients with MS and its clinical correlates. METHODS: Three-hundred and ten consecutive MS patients, seen at our center on either elective or emergent basis, underwent a structured protocol to gather demographics and data about clinical features, previous and current treatments and presence of mood disorders and were additionally assessed by an expert in FND. Patients with and without FND were then compared to identify clinical correlates with the functional comorbidity. RESULTS: Overall, we found that 5.8 % of patients with MS had comorbid FND. Of note, 22.6 % (7/31) of MS patients admitted on an emergent basis for a suspected relapse were found to have incident FND. Patients with comorbid FND had higher rates of clinically significant mood disturbances and a higher number of previous therapeutic switches due to treatment failure or to side effects than patients without FND. Depression, relapsing remitting MS and disability were found to independently predict the presence of FND. CONCLUSIONS: FND is relatively frequent in patients with MS. As the two conditions might have similar phenomenological presentations, it is important to properly screen and recognize FND because of crucial treatment implications.