The aim of this prospective study was to identify the psychiatric morbidity associated with the diagnosis and treatment of early breast cancer. At each of five time points, 269 women were interviewed using a shortened version of the Present State Examination (PSE) and 266 completed self-assessment questionnaires, the Hospital and Anxiety Depression Scale (HADS) and the Rotterdam Symptom Checklist (RSCL). This paper compares the ability of the questionnaires to detect psychiatric morbidity with that of the PSE. The majority of women who experienced anxiety and/or depression did so within 3 months of their initial surgery. The clinical interview identified anxiety disorder in 132 of 266 women (49.6%) and depressive illness in 99/266 (37.2%) during the first 3 months. Using the recommended threshold of > or = 11 for caseness, the sensitivities for both tests were very low at 24.2% (HADS anxiety) and 14.1% (HADS depression) and 30.6% (RSCL psychological distress scale). Lowering the threshold value to > or = 7 on the HADS improved the sensitivity to 72% for the anxiety subscale, but it remained low at 37.4% for the depression subscale. A threshold of > or = 7 for the RSCL scale raised sensitivity to 66.7%. Lowering the threshold values raised the sensitivity of both the instruments but decreased their specificity: the lower the threshold, the greater the number of women who were identified as false positives which would increase the work load for clinic staff if used as a screening tool. Given that the HADS was inadequate in discriminating for depressive illness, it was not surprising that its use as a unitary scale with a threshold value as low as 12 resulted in a sensitivity of only 42.7%. In the light of these findings, we question the use of both the HADS and the RSCL as suitable research or screening instruments for detection of psychological morbidity in early breast cancer.