OBJECTIVES: The purpose of this study was to conduct the first randomized controlled trial (RCT) to evaluate the effectiveness of a second-generation mindfulness-based intervention (SG-MBI) for treating fibromyalgia syndrome (FMS). Compared to first-generation mindfulness-based interventions, SG-MBIs are more acknowledging of the spiritual aspect of mindfulness. DESIGN: A RCT employing intent-to-treat analysis. METHODS: Adults with FMS received an 8-week SG-MBI known as meditation awareness training (MAT; n = 74) or an active control intervention known as cognitive behaviour theory for groups (n = 74). Assessments were performed at pre-, post-, and 6-month follow-up phases. RESULTS: Meditation awareness training participants demonstrated significant and sustained improvements over control group participants in FMS symptomatology, pain perception, sleep quality, psychological distress, non-attachment (to self, symptoms, and environment), and civic engagement. A mediation analysis found that (1) civic engagement partially mediated treatment effects for all outcome variables, (2) non-attachment partially mediated treatment effects for psychological distress and sleep quality, and (3) non-attachment almost fully mediated treatment effects for FMS symptomatology and pain perception. Average daily time spent in meditation was found to be a significant predictor of changes in all outcome variables. CONCLUSIONS: Meditation awareness training may be a suitable treatment for adults with FMS and appears to ameliorate FMS symptomatology and pain perception by reducing attachment to self. Statement of contribution What is already known on this subject? Designing interventions to treat fibromyalgia syndrome (FMS) continues to be a challenge. There is growing interest into the applications of mindfulness-based interventions for treating FMS. Second-generation mindfulness-based interventions (SG-MBIs) are a key new direction in mindfulness research. What does this study add? Meditation awareness training - an SG-MBI - resulted in significant reductions in FMS symptomatology. SG-MBIs recognize the spiritual aspect of mindfulness and may have a role in the treatment of FMS.