Background Posttraumatic stress disorder (PTSD) co-occurs with substance use disorders (SUD) at high rates, but the neurobiological basis of this relationship is largely unknown. PTSD and drug addiction each involve dysregulation of brain reward circuitry, therefore the identification of pathology of the mesolimbic dopamine system may aid in understanding their functional relationship. Dopamine reward dysfunction also may be relevant to the mechanisms underlying the PTSD symptoms of anhedonia and emotional numbing. Methods Single-prolonged stress (SPS) was used as a rat model of PTSD, and a series of behavioral and neuropharmacological assays were applied to assess the impact of SPS on reward, cocaine intake, and components of the striatal dopamine system. Results Exposure to SPS increased anhedonia-like behaviors and decreased the rewarding properties of cocaine compared to control handling. Altered cocaine intake during extended-access self-administration sessions was observed in rats exposed to SPS, further suggesting a difference in the reinforcing properties of cocaine following severe stress. SPS reduced tissue content of dopamine and its metabolites in the striatum, as well as altered striatal dopamine transporter and D2, but not D1, receptor densities. Conclusions These results support a role for altered dopaminergic transmission in reduced reward function in PTSD. Pathology of the dopamine system and the degradation of reward processes may contribute to PTSD symptomology and have implications for co-occurring psychiatric disorders such as substance abuse or depression.