The aim of this study was to determine treatment adherence relative to frequency of violence and posttraumatic stress disorders (PTSD) among new methadone patients. Ninety-six opiate-abusing patients were evaluated for childhood physical and sexual abuse (CPSA), adulthood exposures to violence (ADVIOL), PTSD, and treatment adherence. Overall, 43% of the subjects dropped out of treatment within 3 months of intake. Occurrence of trauma or PTSD did not predict drop-out rates. A 2 (Gender) x 2 (PTSD) analysis of covariance (ANCOVA) with severity of other drug use on admission as a covariate, however, revealed a main effect for PTSD, F(4, 71) = 7. 69, p < or =.01, such that those patients with current PTSD revealed significantly more ongoing drug use at 3 months (M = 24.3, SD = 20. 9) than those without (M = 8.9, SD = 11.8). Examination of ongoing cocaine use using a 2 (Gender) x 2 (PTSD) ANCOVA also revealed a main effect for PTSD, F(4, 17) = 8.24, p < or = .005, such that those patients with current PTSD revealed significantly more ongoing cocaine use at 3 months postadmission (M = 51.6, SD = 37.6) than those without (M = 24.3, SD = 20.9). For both genders, CPSA and ADVIOL were associated with higher rates of PTSD, which in turn predicted poorer treatment adherence as measured by ongoing co-occurring drug abuse 3 months postadmission. Results underscore the need for routine assessment and targeted treatment of trauma in methadone patients.