BackgroundSuicidal ideation (SI) is common in chronic depression, but only limited evidence exists for the assumption that psychological treatments for depression are effective for reducing SI. Methods In the present study, the effects of Mindfulness-based Cognitive Therapy (MBCT; group version) plus treatment-as-usual (TAU: individual treatment by either a psychiatrist or a licensed psychotherapist, including medication when indicated) and Cognitive Behavioral Analysis System of Psychotherapy (CBASP; group version) plus TAU on SI was compared to TAU alone in a prospective, bi-center, randomized controlled trial. The sample consisted of 106 outpatients with chronic depression. Results Multivariate regression analyses revealed different results, depending on whether SI was assessed via self-report (Beck Depression Inventory suicide item) or via clinician rating (Hamilton Depression Rating Scale suicide item). Whereas significant reduction of SI emerged when assessed via clinician rating in the MBCT and CBASP group, but not in the TAU group while controlling for changes in depression, there was no significant effect of treatment on SI when assessed via self-report. Limitations SI was measured with only two single items. Conclusions Because all effects were of small to medium size and were independent of effects from other depression symptoms, the present results warrant the application of such psychotherapeutical treatment strategies like MBCT and CBASP for SI in patients with chronic depression.