Anxiety disorders are the most common type of psychiatric disorders among Western countries. Evidence-based treatment modalities including pharmacological and cognitive-behavioral therapy result in relatively low response rates (average range: 51 – 58%). Historical and recent research suggests psychedelic drugs may be efficacious in alleviating anxiety-related symptoms among healthy and clinical populations. The main aim of the present study was investigation of the effects of psilocybin-containing truffles, when taken in a supportive group setting, on ratings of state and trait anxiety across self-reported healthy volunteers. Attendees of psilocybin ceremonies were asked to complete a test battery at three separate occasions: before the ceremony (baseline), the morning after, and one week after the ceremony. The test battery included questionnaires assessing state and trait anxiety (State-Trait Anxiety Inventory), mindfulness capacities (Five Facet Mindfulness Questionnaire), and personality (Big Five Inventory). Additionally, the psychedelic experience was quantified with the Persisting Effects Questionnaire and the Ego Dissolution Inventory. The total amount of psilocybin-containing truffles consumed by each participant was recorded, and a sample of the truffles was analyzed to determine psilocin concentrations. Fifty-two attendees (males= 25; females= 25; others= 2) completed parts of the baseline assessment, 46 (males= 21; females= 24; others= 1) completed assessments the morning after the ceremony, and 23 (males= 10; females= 13) completed assessments at the one-week follow-up. Average psilocin consumption across individuals was 27.1 mg. We observed medium to large reductions in anxiety measures (both state and trait) compared to baseline which persisted over a one-week period post-ceremony. At one week post-ceremony, the non-judging facet of the mindfulness scale was increased, while the personality trait neuroticism decreased, when compared to baseline. Additionally, we found neuroticism and ratings of ego dissolution to be the strongest predictors of reductions in trait and state anxiety, respectively. In sum, results indicate rapid and persisting (up to one week) anxiolytic effects in psilocybin retreat attendees, which are related to the acute experience of ego dissolution, as well as lasting changes in trait neuroticism. To understand whether these effects extend to wider populations suffering from heightened anxiety, and the mechanisms involved, further experimental research is needed.