Individuals who experience one type of trauma often experience other types, yet few studies have examined the clustering of trauma. This study examines the clustering of traumatic events and associations of trauma with risk for single and co-occurring major depressive disorder (MDD) and panic attack for 20 years after first trauma. Lifetime histories of MDD, panic attack, and traumatic events were obtained from participants in an Australian twin sample. Latent class analysis was used to derive trauma classes based on each respondent's trauma history. Associations of the resulting classes and of parental alcohol problems and familial effects with risk for a first onset of single and co-occurring MDD and panic attack were examined from the year of first trauma to 20 years later. Traumatic events clustered into three distinct classes characterized by endorsement of little or no trauma, primarily nonassaultive, and primarily assaultive events. Individuals in the assaultive class were characterized by a younger age at first trauma, a greater number of traumatic events, and high rates of parental alcohol problems. Members of the assaultive trauma class had the strongest and most enduring risk for single and co-occurring lifetime MDD and panic attack. Assaultive trauma outweighed associations of familial effects and nonassaultive trauma with risk for 10 years following first trauma.