Background If people do not recognize posttraumatic stress disorder (PTSD) symptoms, they may not realize they are suffering from the disorder. Likewise, if people do not know that effective treatments exist, they may be unlikely to seek care. This study examined what people with PTSD symptoms know about PTSD and its treatment. We hypothesized that military service and prior receipt of PTSD treatment would be associated with greater PTSD knowledge. Methods We conducted an online survey assessing knowledge in three domains: trauma, PTSD symptoms, and effective PTSD treatments. Participants were 301 adults (50% veterans) who were drawn from a national research panel and screened positive for PTSD. Results When asked to identify items from a list, participants had better recognition for traumatic events (M = 72.2% of items correct) and PTSD symptoms (M = 62.3%) than for effective PTSD treatments (M = 37.9%). Across domains, participants often identified false items as true. Most participants thought divorce was a trauma that could cause PTSD, that drug addiction was a PTSD symptom, and that support groups are effective PTSD treatments. Prior receipt of PTSD treatment was associated with better symptom recognition (b = .86, P = .003). Being a military veteran was associated with better trauma recognition (b = .56, P = .025), but poorer treatment recognition (b = −.65, P = .034). Conclusions People with PTSD symptoms lack knowledge about the disorder, especially regarding effective treatments. Public education about PTSD is needed so that people recognize when to seek care and which treatments to choose.