Inclusion Criteria:  DSM-5 criteria for chronic PTSD on the Clinician Administered PTSD Scale (CAPS-5) at least moderate PTSD with a total CAPS-5 score of > 26 having had at least one trial of an evidence-based treatment (EBT) for PTSD  Verification of an EBT trial will be by:  subject report of engaging in the EBT (whether it be psycho- or pharmaco-therapy)  CPRS or other medical record system (if outside VA) verification to determine that the dose and time (applies to both meds and therapy) was an adequate trial OR that they clearly did not finish the EBT due to clear aversion  They will be eligible if they did not finish the EBT due to aversion, but they must have had a trial and be fully informed during informed consent for this study of the available clinical treatment options Eligible persons may have other symptoms that are commonly comorbid with PTSD (e.g., anxiety, moderate depression) Severe primary depression will be an exclusion (see "Exclusion criteria" below) This strategy will provide a feasible and generalizable sample Women and minorities will be recruited  Exclusion Criteria:  clear current and past six-months psychosis clearly not related to PSTD hypervigilance, substance dependence (clear evidence of tolerance and/or withdrawal) within the past 6 months thyroid disease and other contraindications to SGB (anatomic abnormalities of the anterior cervical spine; cardiac/pulmonary compromise; acute illness/infection; coagulopathy/bleeding disorder; allergic reactions/contraindications to local anesthetic or contrast dye, prior anterior neck surgery, anterior neck skin abnormalities (rash or eruptions)) decisional incapacity (e.g., dementia, clear evidence of testing that signifies incapacity to consent), OR Montreal Cognitive Assessment score <18 centrally acting medications that have a potential effect on biological expression (detailed in Appendix 10) pain levels requiring opiate medications known exposure to chemicals or physical trauma that cause permanent neuropsychiatric sequelae severe depression (Quick Inventory of Depression-SR16 (QIDS-SR16 score >18) that is deemed more clinically significant than PTSD (i.e., depression, cluster D PTSD, and minimal symptoms from cluster B, C, and E) high risk of acute suicidality  a diagnosed and untreated moderate or severe sleep breathing disorder (SBD), OR a high risk of a SBD as indicated by snoring >50% of nights plus one of  any witnessed apnea feeling non-refreshed in the morning >50% of mornings daytime sleepiness indicated by falling asleep with routine tasks such as watching TV or reading clear treatment non-adherence indicated by stopping treatment or >3 missed appointments in the course of at least three PTSD EBTs past clear and chronic PTSD prior to military service current active psychotherapy for PTSD (they may suspend therapy if chosen by subject and therapist) pregnancy having had any prior SGB unstable dose(s) of medication for depression, anxiety, PTSD, or for sleep, or any other psychoactive medication for 8-weeks prior to intervention  unwillingness to continue active medications at the same doses for the duration of the trial  a person who is on a stable medication dose for > 8 weeks who meets inclusion criteria and will continue these medications for the trial duration will not be excluded