Background Daclizumab has been evaluated in multicentre, randomised, double-blind studies for the treatment of patients with relapsing-remitting multiple sclerosis (RRMS). Safety and tolerability are key considerations in MS treatment selection, as they influence adherence to medication. Objective Evaluate the safety of daclizumab in patients with RRMS from an integrated analysis of six clinical studies. Methods Patients treated with at least one dose of subcutaneous daclizumab 150 mg or 300 mg monthly in three completed and three ongoing clinical studies were included in this integrated analysis. Cumulative incidence of treatment-emergent adverse events (AEs) was the primary endpoint. Results This analysis included 2236 patients with 5214 patient-years of exposure to daclizumab. The cumulative incidence of any AE was 84% and of any serious AE excluding MS relapse was 16%. The incidences of AEs when evaluated by 6-month intervals remained stable over the 6.5 years of maximum follow-up. Most AEs were mild or moderate in severity. An important safety concern associated with daclizumab therapy involved hepatic AEs (16%) and serum transaminase elevations at least three times the upper limit of normal (10%), most of which were asymptomatic, self-limiting, and non-recurring. Cumulative incidences of cutaneous, infectious, and gastrointestinal AEs were 33%, 59%, and 25%, respectively; most events either resolved spontaneously or were treated successfully with standard medical interventions and did not result in discontinuation of treatment. Conclusion This integrated analysis demonstrates that treatment of RRMS with daclizumab for periods of up to 6.5 years is associated with an acceptable safety profile with no evidence of cumulative toxicity over time.