Posttraumatic stress disorder (PTSD) is a prevalent disorder worldwide and often co-occurs in dementia. Both have a major impact on disease burden and quality of life. PTSD may be difficult to recognize in dementia and a structured diagnostic method is lacking. In order to get insight into the clinical diagnostics of PTSD in dementia, this systematic literature review evaluates the clinical presentation of PTSD and other relevant symptoms in people with dementia. PubMed, PsycINFO, Embase, and CINAHL were searched for all publications through 30 December 2021. Articles were included which met the following criteria: (i) description of at least one case with a current diagnosis of dementia and co-morbid PTSD; (ii) clinical presentation of symptoms being adequately described; (iii) no difference being made between chronic PTSD, PTSD with re-activation, and delayed onset PTSD. Of the 947 identified abstracts, 13 papers met the inclusion criteria and were included (describing 30 cases). Based on our rating, only one case completely fulfilled the DSM-5 criteria of PTSD. Avoidance was only described in three cases. Most commonly described symptoms were irritability and anger (E1, 9%), persistent negative emotional state (D4, 9%), and sleep disturbances (E6, 8%). In 93% of the case reports, other symptoms were also described, i.e. memory problems (58%), screaming (33.3%), and wandering (22.2%). People with dementia who have experienced a traumatic event seem to present, based on our rating method, with insufficient symptoms to meet all criteria for a PTSD DSM-5 diagnosis. The DSM-5 core symptom of avoidance was absent in most of the cases. Clinical presentation consists mainly of symptoms of irritability, anger, persistent negative emotional state, and sleep disturbances, often accompanied by other symptoms. These findings suggest that older people with dementia may have other symptom presentations than people without dementia.