The symptom presentation of posttraumatic stress disorder (PTSD) varies widely between individuals, which can complicate both diagnosis and treatment. Personality may help to explain this variability, and personality-based subtypes of PTSD (externalizing, internalizing, and simple; Miller, Greif, & Smith, 2003) have been identified for this purpose. Yet, empirical tests of these subtypes have been limited, focusing largely on older samples with combat trauma or other homogenous trauma types. Our study examined PTSD subtypes in two samples of young adults with heterogeneous trauma exposure using cluster analyses. We tested for subtype-based heterogeneity in traumatic response (i.e., PTSD symptomatology). Results revealed that, across the two samples, externalizing (low conscientiousness and moderate neuroticism), internalizing (low extraversion and moderate neuroticism), and simple (low neuroticism) personality-based subtypes emerged, consistent with the existing literature. Subtype-based differences in PTSD symptom severity also were observed, with the simple subtype generally exhibiting less severe PTSD symptomatology than internalizing and externalizing subtypes. However, the subtypes did not differ in terms in number or type (interpersonal vs. noninterpersonal) of traumatic experiences. Findings support PTSD subtypes and their relevance for posttraumatic response, particularly PTSD severity, in young adults with a variety of trauma types.