["Clinical Psychology &Psychotherapy, Volume 33, Issue 3, May/June 2026. ", "\nABSTRACT\nThe feasibility of psychological interventions should be considered when developing and evaluating new therapy methods. Indicators of low feasibility may be a high dropout rate, a low attendance rate and low treatment satisfaction, which threaten the validity of clinical research studies. Given the severity and chronicity of bipolar disorder and its impact on psychosocial functioning, effective treatments are needed to alleviate depressive and manic symptoms. The study evaluated the feasibility and preliminary treatment effects of a novel disorder‐specific metacognitive group training for bipolar disorder (MCT‐Bipolar), which targets cognitive biases specific to depressive and manic episodes while also incorporating mindfulness techniques. Forty‐eight outpatients with bipolar disorder I and II participated in the training conducted by a clinical psychologist for eight consecutive weeks in groups of six to 10 people. Inclusion criteria were euthymia or mild or moderate depressive symptoms. Predictors of dropout and attendance rates were analysed using regression methods, and secondary exploratory analyses examined changes in various efficacy indicators between baseline, 1 week after training and 6 months after training using linear mixed models. In total, 10 participants (20.8%) dropped out, while completers attended an average of six out of eight sessions. Treatment satisfaction of the completers was high. Linear mixed models revealed an increase in mindfulness from baseline to follow‐up. Results on psychosocial functioning showed an increase from baseline to post‐training, though this effect disappeared at the 6‐month follow‐up. Findings support the feasibility of MCT‐Bipolar and suggest potential benefits for mindfulness and short‐term psychosocial functioning. Further research with larger samples and a control group is needed to assess its efficacy.\nTrial Registration: The evaluation study is registered in the German Registry of Clinical trials (DRKS, registration number DRKS00035704) and received approval from the ethical committee of Charité – University Hospital Berlin (No. EA1/076/22).\n"]