Dialectical behavior therapy (DBT) is a treatment for borderline personality disorder, a disorder for which emotion dysregulation is central. Within DBT, there are 6 explicitly defined validation strategies that range hierarchically from validation level (VL) 1 to VL 6. To date, there have been no studies on the frequency of use of VLs in actual DBT sessions. The aim of the current study was to explore DBT therapists’ use of VLs and examine the relationship between VLs and change in a client emotion during therapy sessions. DBT treatment sessions (n = 121) across 35 participants in a DBT training clinic were coded for therapist use of VLs. A repeated-measures analysis of variance (ANOVA) was used to assess for change in therapist use of VLs over time and hierarchical linear modeling was used to correlate therapist use of these strategies with change in client emotion. Results indicated no significant relationship between overall frequency of VLs and change in client emotion. However, an increase in frequency of high VLs was associated with an increase in positive affect (PA) and a decrease in negative affect (NA) while an increase in frequency of low VLs was associated with a decrease in PA and no change in NA. An increase in frequency of VL 4 was associated with an increase in NA. VL 6 was associated with an increase in PA and a decrease in NA. Findings suggest that specific validation strategies may be related to session changes in affect and have implications for identifying potential mechanisms of change.