Dissociative experiences are common among people presenting with post-traumatic stress disorder, yet they are often not elicited by routine assessment. This narrative review distinguishes three situations that are frequently conflated: dissociative symptoms occurring within PTSD, the dissociative subtype of PTSD, and dissociative disorders — other specified dissociative disorder and dissociative identity disorder — diagnosed alongside PTSD. It examines why clinically significant dissociation may go unrecognized, separating what a patient experiences, what the patient is able or willing to disclose, and what the clinician asks, and it notes that diagnostic criteria are not designed to exhaust the phenomenology of dissociation, so that a criterion-focused interview may leave relevant experiences unexplored. Structural dissociation theory is presented as one clinical model for understanding discontinuities in self-experience, not as an equivalence between diagnoses. The review then considers how dissociative presentations may coexist with, be mistaken for, or resemble psychotic, bipolar, borderline, and depressive disorders, framing each as a question of when further assessment for dissociation is warranted. It proposes a conditional, tiered assessment pathway — self-report screening, qualitative follow-up, phenomenological inventory, structured diagnostic interview, and longitudinal observation — with attention to the sensitivity limits of each step; the pathway has not been validated. Finally, it discusses potential implications for treatment planning, distinguishing PTSD with dissociative symptoms from complex dissociative disorders and noting that findings on dissociation as a predictor of trauma-focused treatment outcome are mixed.