The current study assessed the incidence and associated features of posttraumatic stress after the experience of panic. One hundred seventy-eight participants meeting diagnostic criteria for panic attacks (PAs) were assessed using standardized measures of posttraumatic symptoms and posttraumatic stress disorder (PTSD) in specific reference to their experience of panic. Sixty-three (35.4%) participants scored above the cutoff for PTSD in reference to the worst PA they had experienced. Adjusted means for the four PTSD symptom clusters indicate that panic-related posttraumatic symptoms are, on average, experienced “moderately” to “quite a bit.” Panic-related posttraumatic symptoms and PTSD were best predicted by specific features of the panic experience itself, including subjective levels of distress, fear of losing control, chest pain, agoraphobia, and number of PAs experienced. These findings are discussed in terms of the diagnostic, prognostic, and treatment implications for a subset of individuals presenting with panic who may also have panic-related PTSD.