Psychedelic experiences involving extreme feelings of horror, helplessness, and perceived threats can be traumatizing. Traumatic psychedelic experiences are a rare, extreme, and largely preventable form of challenging experience which can arise due to frightening psychedelic drug effects, unsafe settings, and emergence of pre-existing trauma. Some people recover quickly, but others develop prolonged anxiety, sleep disturbances, derealization, or other potentially trauma-related symptoms. This chapter discusses the causes, phenomenology, and potential outcomes of traumatic psychedelic experiences, as well as how to prevent them and minimize their negative impact.