"Functional somatic symptom disorders (FSSDs) are defined by persistent and chronic bodily complaints without a pathological explanation. Mindfulness involves the focus on the present moment by noticing surroundings, thoughts, feelings, and events, being nonreactive, being non-judgemental, and self-accepting. Psychological flexibility (PF) involves a focus on the present and the prioritization of thoughts, emotions, and behaviours that align with individual values and goals (Francis et al., 2016). Although PF does not involve a mindfulness practice, the two constructs are related. Research indicates consistent reported positive associations between mindfulness, PF, psychological wellbeing, and medical symptoms. In this study, individuals with FSSDs (fibromyalgia, chronic fatigue syndrome) were compared to those with well-defined autoimmune illnesses (multiple sclerosis, rheumatoid arthritis; AD) to determine how psychosocial factors affect wellness. Participants (N = 609) were recruited from social media and online support groups and completed questionnaires to assess physical health (Chang et al., 2006), psychological wellness (Diener et al., 1985), anxiety (Spitzer et al., 2006), depression (Martin et al., 2006), psychological flexibility, (Francis et al., 2016) and mindfulness (Droutman et al., 2018]. Results indicated that having an FSSD and higher depression was associated with both lower physical and psychological wellness. Interestingly, different aspects of psychological flexibility predicted physical and psychological wellness. These results suggest that different aspects of PF are associated with better physical and psychological health. As PF is modifiable, individuals with chronic conditions could receive training that could ultimately improve their overall health."