Background: The recent randomized, controlled trial of interferon-β1b (IFN-β1b) in 718 patients with secondary progressive MS (SP-MS) demonstrated a significant effect on the development of disability as evaluated by the physician. Its effect on patient-reported health-related quality of life (HrQoL) is reported herein. Methods: In this multicenter, double-blind, randomized, placebo-controlled trial, outpatients with SP-MS scoring between 3.0 and 6.5 on the Expanded Disability Status Scale received either 8 × 106 IU of IFN-β1b or placebo for up to 3 years. A range of outcomes was measured, including HrQoL, which was assessed using the Sickness Impact Profile (SIP), a self-report questionnaire validated for use in MS. Measurements were undertaken at baseline and at 6-monthly intervals thereafter for 36 months. Results: A slight positive effect on the HrQoL of the IFN group in comparison with the placebo group was found, which reached significance in the physical scale of the SIP at 6 and 12 months and at last visit. There was moderate correlation between physician-assessed evaluation of change and patient-reported change. Conclusions: IFN-β1b may delay sustained deterioration in patient-reported HrQoL in SP-MS. Methods of interpreting change in HrQoL are currently insufficiently developed to determine how clinically important these changes are for this population.