The authors review sample composition and enrollment data for 34 studies cited in the International Society for Traumatic Stress Studies (ISTSS) 2000 Practice Guidelines as meeting the Level A U.S. Agency for Health Care Policy and Research (AHCPR) classification for treatment of adult posttraumatic stress disorder (PTSD), and compare data from more recent research. Findings reveal that many published reports omitted vital data including exclusion criteria and rates, demographics, and trauma exposure history. Moreover, severe comorbid psychopathology, a common feature of treatment-seeking individuals with PTSD, emerged as the predominant reason for exclusion across studies. Subsequently published studies exhibited improved reporting of sample characteristics and demonstrated comparable outcomes despite inclusion of more diverse trauma exposure samples. Findings indicate the need for future efficacy research to adopt more comprehensive reporting requirements and to test the applicability of validated treatments to individuals suffering from as yet unstudied combinations of PTSD and prevalent comorbid disorders.