There are few published data from real-world clinical experience with miglustat (Zavesca), an oral inhibitor of glucosylceramide synthase, in type 1 Gaucher disease. We report data from a prospective, open-label investigational study that evaluated substrate reduction therapy with miglustat 100 mg t.i.d. as a maintenance therapy in patients with Type 1 Gaucher disease who had been switched from previous enzyme replacement therapy. Long-term data on changes in organ size, blood counts, disease severity bio-markers, bone marrow infiltration, overall clinical status and safety/tolerability were analyzed from 28 patients with Type 1 Gaucher disease who were attending routine clinic visits. Assessments were performed at six, 12, 24, 36 and 48 months of therapy. Disease severity biomarkers improved up to 48 months after initiation of miglustat, while other disease parameters remained stable. Miglustat showed an acceptable profile of safety and tolerability throughout treatment. In conclusion, miglustat is an effective therapy for the long-term maintenance of patients with Type 1 Gaucher disease previously stabilized with enzyme replacement therapy.