Cognitive behavioural therapy (CBT) is a recommended treatment for unipolar depression, and a large number of studies provide supportive evidence for its efficacy in both an individual as well as a group format [
1‐
3]. CBT has been shown to be effective in the short term and to have enduring effects in reducing the risk of returning symptoms after treatment has ended. However, approximately one third of the patients do not respond satisfactorily to the treatment [
4,
5], and post-treatment residual symptoms are a common problem; as many as 30–50 % of remitted patients experience residual symptoms at the end of treatment [
6]. Residual symptoms of depression are associated with ongoing psychosocial and functional disability and have been demonstrated to predict poorer long-term outcome of major depression, including increased rates of relapse [
7‐
9]. A recent meta-analysis reports relapse rates of around 29 % within 1 year and 56 % within 2 years [
10].
Recent studies have evaluated the potential benefit of continuation-phase CBT in reducing residual symptoms as well as in preventing subsequent depressive relapse or recurrence. In general, continuation-phase cognitive therapies have proven to be beneficial in reducing rates of relapse and recurrence [
10]. Yet, in most of these studies, only a modest reduction in residual symptoms was observable [
11,
12], indicating the possibility of further improvement in efficacy by targeting key residual symptoms. With the aim of improving efficacy, an increased focus has been directed toward a common residual symptom, namely depressive rumination [
13,
14]. Rumination is a passive process of recurrent negative thinking and dwelling on negative affect, causes, and symptoms [
15] and has been shown to be a major factor in vulnerability to depression as well as predicting the onset, severity, and duration of future depressive episodes [
16,
17]. Consequently, if involved in the pathogenesis of depression, rumination may constitute a relevant target for psychological intervention. In support of this, recent psychotherapeutic interventions designed to target depressive rumination show promising results [
18‐
20]. The strongest evidence thus far exists for the rumination-focused cognitive behavioural therapy (RFCBT) developed by Watkins and colleagues [
18]. RFCBT is based on a conceptualization of repetitive thinking that differentiates between a functional and a dysfunctional style of thinking. The helpful style is characterized by being concrete and specific, whereas the unhelpful style is abstract and evaluative and does not lead to problem solving (rumination) [
21]. In RFCBT, rumination is formulated as a habitual behaviour controlled by the laws of behavioural psychology [
22] and maintained by negative reinforcement. Rumination can act as a form of avoidance by thinking about difficulties rather than confronting them directly in the real world and thereby avoiding the risk of failure and negative outcomes. Hence, rumination can become reinforced by escape and avoidance. Grounded in behavioural psychology and research, RFCBT focuses on functional analyses of the target behaviour, rumination, and combines strategies from behavioural activation with novel strategies to foster concrete, process-focused, and specific thinking. RFCBT differs from standard CBT by focusing on modifying the process of thinking, whereas CBT focuses on modifying the content of the thoughts and content of dysfunctional schemas [
14]. With only a handful of trials conducted, the evidence for RFCBT is still sparse, although it is promising. For example, in a recent clinical trial with patients with medication-refractory residual depression, 42 patients were randomly allocated (1:1) to treatment-as-usual (TAU) consisting of continuation anti-depressants and outpatient clinical management or to TAU plus up to 12 sessions of individual RFCBT. RFCBT was found to be superior to TAU; 62 % of patients in the RFCBT treatment condition achieved remission, compared with 21 % in the TAU [
18]. However, to date, no study has made a direct comparison of RFCBT with standard CBT. The aim of the present study is to compare group-based rumination-focused cognitive behaviour therapy (g-RFCBT) with group-based standard cognitive behavioural therapy (g-CBT) for depression on the effectiveness of treatment and the reduction of relapse rates at 6-month follow-up.