ABSTRACT: Background:Psilocybin therapy has shown promise as a rapid-acting treatment for depression, anxiety, and demoralization in patients with serious medical illness (e.g., cancer) when paired with individual psychotherapy. This study assessed the safety and feasibility of psilocybin-assisted group therapy for demoralization in older long-term AIDS survivor (OLTAS) men, a population with a high degree of demoralization and traumatic loss. Methods:Self-identified gay men OLTAS with moderate-to-severe demoralization (Demoralization Scale-II ?8) were recruited from the community of a major US city for a single-site open-label study of psilocybin-assisted group therapy comprising 8-10 group therapy visits and one psilocybin administration visit (0·3-0·36?mg/kg po). Primary outcomes were rate and severity of adverse events, and participant recruitment and retention. The primary clinical outcome was change in mean demoralization from baseline to end-of-treatment and to 3-month follow-up assessed with a two-way repeated measures ANOVA. Trial registration: Clinicaltrials.gov (NCT02950467). Findings:From 17 July 2017 to 16 January 2019, 18 participants (mean age 59·2 years (SD 4·4)) were enrolled, administered group therapy and psilocybin, and included in intent-to-treat analyses. We detected zero serious adverse reactions and two unexpected adverse reactions to psilocybin; seven participants experienced self-limited, severe expected adverse reactions. We detected a clinically meaningful change in demoralization from baseline to 3-month follow-up (mean difference -5·78 [SD 6·01], ?p 2?=?0·47, 90% CI 0·21-0·60). Interpretation:We demonstrated the feasibility, relative safety, and potential efficacy of psilocybin-assisted group therapy for demoralization in OLTAS. Groups may be an effective and efficient means of delivering psychotherapy pre- and post-psilocybin to patients with complex medical and psychiatric needs. Funding:Carey Turnbull, Heffter Research Institute, NIMH R25 MH060482, NIH UL1 TR001872, River Styx Foundation, Saisei Foundation, Sarlo Foundation, Stupski Foundation, Usona Institute, US Department of Veterans Affairs (Advanced Neurosciences Fellowship and IK2CX001495).