To investigate differences between patients whose posttraumatic stress disorder (PTSD) preceded their cocaine dependence and vice versa, 33 patients with comorbid PTSD and cocaine dependence were divided into two groups: one in which the traum and PTSD occurred before onset of cocaine dependence (primary PTSD) and one in which the PTSD occurred after cocaine dependence was established (primary cocaine). In the primary-PTSD group, the trauma was generally childhood abuse. In the primary-cocaine group, the trauma was generally associated with the procurement and use of cocaine. In the primary PTSD group, there were significantly more women, more other Axis I diagnoses, more Cluster B and C Axis II diagnoses, and more benzodiazepine and opiate use. In the primary-cocaine group, there was a trend toward more cocaine use in the previous month. Significant clinical differences between these two groups may warrant different types of treatment or differing treatment emphasis.