A screening programme designed to identify cases of Major Depressive Disorder (MDD) in patients attending a Regional Cancer Centre outpatient department was established. It comprised two stages: (1) The Hospital Anxiety and Depression Scale (HADS) self-rating questionnaire administered by a touch-screen computer; (2) we interviewed patients with high scores on the HADS (15 or more total score) over the telephone using the depression section of the Structured Clinical Interview for DSMIV (SCID). A large consecutive sample (5613) of oncology clinic attenders was screened, and practical difficulties in the screening process were identified. The estimated prevalence of major depressive disorder (MDD) in the sample surveyed was approximately 8% (7.8%; 95% confidence intervals 6.9-8.5%). We assessed a consecutive series of 150 patients identified as having MDD to determine how many had received evidence-based treatment for MDD. Only half had discussed their low mood with their general practitioner, only one-third had been prescribed any antidepressant medication, and very few had taken a therapeutic dose for an adequate period. Very few had received psychological treatment or had been referred to mental health services. Most were receiving no potentially effective therapy.