Background <p>Despite significant advances in the treatment of posttraumatic stress disorder (PTSD), heterogeneity in symptom presentation and high rates of comorbidity with other mental health conditions may limit the acceptability and efficacy of existing interventions. Idiographic approaches have been proposed as one solution to these challenges and may offer opportunities to improve treatment outcomes.</p> Methods <p>The present study used ecological momentary assessment (EMA) to assess momentary PTSD symptoms (i.e., re-experiencing, avoidance, negative cognitions and mood, and arousal) and commonly co-occurring symptoms (i.e., depression, anxiety, impulsive behavior/substance use, and emotion dysregulation) among undergraduates with probable PTSD (<i>N</i> = 25). Contemporaneous and temporal idiographic networks were estimated for each participant and centrality metrics were then used to identify the most influential symptoms in each network.</p> Results <p>While negative cognitions were among the most central (i.e., influential) symptoms for nearly 50% of the sample, results indicated substantial heterogeneity in symptom presentation. Exemplar cases are used to illustrate how results of these networks could be used to select the optimal trauma-focused interventions (i.e., cognitive processing therapy or prolonged exposure) or tailor transdiagnostic approaches (e.g., the Unified Protocol).</p> Conclusions <p>Idiographic approaches offer promise for treatment selection and personalization for individuals with PTSD and comorbid conditions.</p>