Objectives: To examine reductions in suicidal ideation among a sample of patients who were prescribed an internet cognitive behavior therapy (iCBT) course for depression. Design: Effectiveness study within a quality assurance framework. Setting: Primary care. Participants: 299 patients who were prescribed an iCBT course for depression by primary care clinicians. Intervention: Six lesson, fully automated cognitive behaviour therapy course delivered over the internet. Primary outcome: suicidal ideation as measured by question 9 on the Patient Health Questionnaire (PHQ-9). Results: Suicidal ideation was common (54%) among primary care patients prescribed iCBT treatment for depression but dropped to 30% post-treatment despite minimal clinician contact and the absence of an intervention focused on suicidal ideation. This reduction in suicidal ideation was evident regardless of sex and age. Conclusions: The findings do not support the exclusion of patients with significant suicidal ideation.