Based on their presumed immuno-mediated etiology, post-infectious CNS disorders are commonly treated with high-dose steroids. Factors influencing treatment effectiveness, possible alternative options for steroid-resistant cases, and their outcome profiles, remain unclear. We here describe the clinical features, the prognosis and the efficacy of i. v. immunoglobulins (IVIg) in a series of severe ADEM refractory to steroids. We performed an inception cohort study on inpatients of the Neurologic and Infectious Disease Clinics, consecutively admitted over eight years, with a minimum two-year follow-up. Nineteen patients affected by classic and site-restricted ADEM were treated with IVIg after steroid failure. Five other patients received IVIg as first-line treatment due to steroids contraindications: although not included in the analysis, they were monitored for anecdotal comparison. Steroids were administered as IV 6-methylprednisolone (6-MP) 500/1000 mg daily until a maximum dose of 6–8 g; IVIg were administered at 0.4 g/kg/day for 5 days. The outcome was assessed by the Scripps Neurological Rating Scale (SNRS) score with determined periodicity. We observed that steroid-resistant patients showed high prevalence of PNS damage (89%) and myelitis (95 %). Other features were old age, severe disability at onset, and moderate to severe blood-brain-barrier (BBB) damage on CSF. In 10/19 patients (53 %) IVIg were effective, the clinical improvement beginning within the end of the five-day cycle,without relapses. Prominent effects of IVIg were detectable on motor dysfunction. Milder onset disability (p = 0.013) and lower CSF albumin (p = 0.006) were the predictors of IVIg response.Among steroid-free patients, 3/5 were responsive to IVIg. We conclude that IVIg can be useful in a portion of patients with severe steroid-resistant ADEM and prominent motor dysfunction. Unsolved issues regard the usefulness of IVIg in less selected groups, and the spectrum of their clinical effects.