No studies have been conducted yet into the effectiveness of treatment of personality disorders in later life. This study is a first test of the effectiveness of schema therapy for personality disorders in older adults. Multiple-baseline design with eight cluster C personality disorder patients, with a mean age of   69. After a baseline phase with random length, schema therapy was given during the first year, followed by follow-up sessions during six months. Participants weekly rated the credibility of dysfunctional core beliefs. Symptomatic distress, early maladaptive schemas, quality of life and target complaints were assessed every six months and personality disorder diagnosis was assessed before baseline and after follow-up. Data were analyzed with mixed regression analyses. Results revealed significant linear trends during treatment phases, but not during baseline and follow-up. The scores during follow-up remained stable and were significantly lower compared to baseline, with high effect sizes. Seven participants remitted from their personality disorder diagnosis. Schema therapy appears an effective treatment for cluster C personality disorders in older adults. This finding is highly innovative as this is the first study exploring the effectiveness of psychotherapy, in this case schema therapy, for personality disorders in older adults.