Many adult cancer survivors experience persistent emotional distress after completing cancer treatment. The aim of this study was to test the potential of a brief transdiagnostic psychological intervention-metacognitive therapy (MCT)-in reducing emotional distress in adult cancer survivors. A non-concurrent multiple baseline design with 3- and 6-months follow-up was used to evaluate the effects of MCT in four patients consecutively referred to a psycho-oncology service. Each patient received six 1-h sessions of MCT. Anxiety, depression, worry/rumination, fear of cancer recurrence and metacognitive beliefs were assessed using self-report questionnaires. MCT was associated with clinically significant reductions in anxiety, depression, fear of cancer recurrence, worry/rumination and metacognitive beliefs at the end of treatment, and gains were maintained in all patients to 3-months follow-up and in three out of four patients to 6-months follow-up. MCT is a promising brief transdiagnostic approach to psychological morbidity in adult survivors of cancer. Larger scale controlled trials are now required.