Background and Objectives: Poor sleep is prevalent among individuals with social anxiety disorder (SAD) and may affect treatment outcome. We examined whether: (1) individuals with SAD differed from healthy controls (HCs) in sleep quality, (2) baseline sleep quality moderated the effects of treatment (Cognitive-behavioral group therapy [CBGT] vs. mindfulness-based stress reduction [MBSR] vs. waitlist [WL]) on social anxiety, (3) sleep quality changed over treatment, and (4) changes in sleep quality predicted anxiety 12-months post-treatment. Design: Participants were 108 adults with SAD from a randomized controlled trial of CBGT vs. MBSR vs. WL and 38 HCs. Methods: SAD and sleep quality were assessed pre-treatment and post-treatment; SAD was assessed again 12-months post-treatment. Results: Participants with SAD reported poorer sleep quality than HCs. The effect of treatment condition on post-treatment social anxiety did not differ as a function of baseline sleep quality. Sleep quality improved in MBSR, significantly more than WL, but not CBGT. Sleep quality change from pre- to post-treatment in CBGT or MBSR did not predict later social anxiety. Conclusions: MBSR, and not CBGT, improved sleep quality among participants. Other results were inconsistent with prior research; possible explanations, limitations, and implications for future research are discussed. ClinicalTrials.gov identifier: NCT02036658.