Past research demonstrated that age at onset might account for different clinical and etiological characteristics in panic disorder (PD). However, prior research relied on arbitrary choices of age cut-offs. Using a data-driven validated method, this study aimed to examine differences between early and late onset PD in various determinants. Admixture analysis was used to determine the best fitting model of age at onset distribution in PD. Data was collected from 511 individuals (ages 18-65) with PD diagnoses, who participated in the Netherlands Study of Depression and Anxiety (NESDA). DSM-IV comorbidities and various measures of childhood adversities, suicidal behavior, anxiety and depressive symptoms were assessed. The best fitting cut-off score between early and late age at onset groups was 27 years (early age at onset