This study examined whether insomnia persisted after completion of cognitive behavioral therapy (CBT) for PTSD and whether persistence of insomnia was associated with continuing nightmares, vigilance, depression, childhood abuse history, or having been traumatized in a sleep-related context. A retrospective analysis of posttreatment Clinician-Administered PTSD Scale (CAPS) data from 27 patients who no longer met PTSD diagnosis following CBT for PTSD revealed that 48% reported residual insomnia. For the large majority, insomnia persisted in the absence of continuing nightmares and hypervigilance. Experiencing trauma in a sleep-related context was associated with greater risk for residual insomnia, whereas childhood abuse history and depression were not. These findings suggest that interventions to address factors maintaining insomnia residual to PTSD warrant study.