RESUMEN
This study investigated the effectiveness of brief individual experiential schema therapy (ST) in 12 adult outpatients with cluster C personality disorders (PD) using randomised multiple baseline design. Waitlist period was followed by five explorative sessions, 18 experiential ST sessions, two treatment follow-up (FU) booster sessions and a 6-month FU assessment. Overall well-being (ORS), behavioural treatment goals and negative core beliefs were assessed 60-91 times, global symptomatic distress (BSI) six times. PD severity (SCID-5-PD) was pre-post-analysed. Randomisation and non-parametric tests showed large significant effects (d = 1.08-2.38, r = .53-.66) on all outcomes at treatment-FU and 6-month FU assessment. This is the first study providing preliminary evidence of effectiveness of brief individual experiential ST for patients with cluster C PD, tentatively challenging the common tenet that long treatment duration is required. Due to limitations, replication is recommended.