INTRODUCTION:The present study examined seizure clusters as a primary outcome in patients receiving treatment for PNES. Cluster reduction is examined longitudinally using frequency threshold and statistical definitions of seizure cluster for patients. Possible risk factors for clustering will be examined along with clustering as a risk factor for poorer secondary outcomes. METHODS:Participants were from a pilot randomized treatment trial for PNES where they received cognitive behavioral therapy-informed psychotherapy (CBT-ip), sertraline, combination therapy, or treatment as usual. Seizure data are from patients' seizure dairies. RESULTS:Cluster reduction was observed for those receiving CBT-ip or combination treatment using all definitions of daily clusters and weekly clusters. No risk factors of clustering were observed. Those who were identified as having clusters during the trial had poorer secondary outcomes on several measures at baseline relative to those who were not identified as having clusters. DISCUSSION:This is the first study known to the authors to not only examined seizure clusters as a primary outcome for those with PNES, but also the first study to suggest that CBT-ip and combination therapy may be effective in reducing the frequency of clusters.