Objective: Multiple sclerosis (MS) is a chronic neurodegenerative disease which is the second most frequent cause of neurological disability in young adults. The relapsing forms of the disease are primarily treated with interferon beta or glatiramer acetate. The aim of this study was to evaluate the level of satisfaction of Spanish MS patients treated with the new formulation of Avonex®, and whether this influences adherence. Methods: Data were obtained from the Global Adherence Project, a multicenter open-label, post-marketing surveillance study, performed in 17 centers in Spain. This included assessment of the level of patient and neurologist satisfaction with the new Avonex® formulation after 6 months of therapy. Two questionnaires were administered, one for patients and another for neurologists. The study was approved by ethics committees and patients signed informed consent. Descriptive statistical analyses were performed. Results: Of 257 patients included, 57 (22.2%) were treated with Avonex®; 55.4% of patients and 5.9% of neurologists were fully satisfied with the new formulation. Most neurologists (88.3%) had intermediate satisfaction scores. For patients and for neurologists, the most noteworthy aspect of the change of formulation was the ease of use (73.2% and 82.4%, respectively), followed by ease of storage (44.6% and 29.4%), ease of injection (39.3% and 70.6%), less medication administered (25.0% and 11.8%) and for patients only, better tolerability (8.9%). Adherence with Avonex® was 96.4%, the highest among the therapies evaluated. Conclusion: Both patients and neurologists were satisfied with Avonex® as solution for injection. The most noteworthy aspect was the ease of use. This seems to have a positive influence in the overall patients' adherence to the therapy.