Altered cortisol has been demonstrated to be lower in those with posttraumatic stress disorder (PTSD) in most studies. This cross-sectional study evaluated salivary cortisol at waking and 30 minutes after, and at bedtime in 51 combat veterans with PTSD compared to 20 veterans without PTSD. It also examined the relationship of cortisol to PTSD symptoms using 2 classifications: the Diagnostic and Statistical Manual of Mental Disorders (4th ed., DSM-IV; American Psychiatric Association, 1994) and the more recent 4-factor classification proposed for DSM-5. The PTSD group had lower cortisol values than the control group, F(6, 69) = 3.35, p = .006. This significance did not change when adding age, body mass index, smoking, medications affecting cortisol, awakening time, sleep duration, season, depression, perceived stress, service era, combat exposure, and lifetime trauma to the model. Post hoc analyses revealed that the PTSD group had lower area-under-the-curve ground and waking, 30 min, and bedtime values; the cortisol awakening response and area-under-the-curve increase were not different between groups. The 4-factor avoidance PTSD symptom cluster was associated with cortisol, but not the other symptom clusters. This study supports the finding that cortisol is lower in people with PTSD.