Treatment nonadherence is a concern among patients with bipolar disorder and posttraumatic stress disorder (PTSD). PTSD is common among patients with bipolar disorder and those with this comorbidity often have a more severe course of illness. While many factors have been associated with nonadherence in bipolar disorder patients and in PTSD patients, almost no research has focused on the factors associated with non-adherence in bipolar disorder patients with comorbid PTSD. Studies in primary bipolar disorder samples reveal patient, illness, drug and clinician characteristics associated with nonadherence while studies in primary PTSD samples reveal a significantly shorter list of patient, illness and drug characteristics. Shared risk factors between these two populations and the characteristics that predict noncompliance in only one population but often present in the other, suggest a high likelihood of nonadherence in the bipolar disorder-PTSD population. For bipolar disorder-PTSD patients with early childhood trauma, noncompliance may be related to the trauma-related meanings attributed to interactions with their physicians and their prescribed medications. Given the high side effect burden of bipolar disorder treatments and the importance of lifelong adherence, clinicians should vigilantly monitor for nonadherence in their bipolar disorder-PTSD patients and be particularly aware of patient-physician psychodynamics that might contribute to this behavior.