Psychological inflexibility and emotional dysregulation are a hallmark of psychopathology, being intrinsically embedded in emotional and personality disorders. However, the transdiagnostic mechanisms of psychological inflexibility and emotional dysregulation domains are still a matter of discussion.

The present study aims to explore the relationships between cognitive fusion (as a measure of psychological inflexibility), emotion regulation strategies, such as cognitive reappraisal and emotional suppression and emotional dysregulation domains in two different samples.

In a cross-sectional design, 297 individuals were assessed with self-report measures and divided into non-clinical (n = 231) and clinical samples (n = 66), according to diagnosis.

Results showed that the degree of cognitive fusion was higher in the clinical sample. However, significant correlations between cognitive fusion, emotional regulation strategies and emotional dysregulation domains were found in the two samples. Cognitive reappraisal and emotional dysregulation domains predicted cognitive fusion and mediated the relationship between cognitive fusion and symptomatology in the two samples.

Relationships between cognitive fusion and emotional dysregulation domains were found independent of diagnosis. The implementation of emotion regulation strategies may be related to individual differences. However, cognitive fusion, reappraisal and lack of strategies may be core transdiagnostic features in psychological inflexibility and emotion dysregulation.