BackgroundCognitive Behavioral Social Rhythm Group Therapy (CBSRT) is a chronobiologically-informed group therapy designed to stabilize social rhythms in veterans with comorbid combat-related PTSD and major depressive disorder (MDD). This randomized controlled pilot trial is the first to examine feasibility and preliminary efficacy of group CBSRT as compared to group Present Centered Therapy (PCT), a well-characterized active attention, psychotherapy condition. MethodsA total of 43 male veterans with combat-related PTSD, MDD, and disruptions in sleep or daily routine were randomly assigned to CBSRT or PCT. Therapy was provided weekly in a group modality for 12 weeks. Follow-up feasibility and gold-standard PTSD, MDD, and subjective/objective sleep assessments were conducted at post-treatment, 3 months, and 6 months post-treatment. ResultsFeasibility results demonstrated that veterans assigned to CBSRT had higher rates of attendance than veterans assigned to PCT. Both CBSRT and PCT were associated with improvements in PTSD and MDD symptoms, sleep efficiency, and number of awakenings; there were no differences between group therapies on these indices. Veterans in the CBSRT group had a greater reduction in the number of nightmares than veterans in the PCT group. LimitationsPreliminary results must be qualified by the small sample size. ConclusionsGroup CBSRT may be more feasible for veterans than PCT. Both CBSRT and PCT were associated with improvements in psychiatric symptoms with few differences between conditions. CBSRT is a promising new group therapy that may help address the high-rate of PTSD therapy attrition in combat veterans. Clinical trial registrationNCT00984698.