Background: Although depression is often reported in prostate cancer patients, some tests of depression omit the somatic criteria that are listed for Major Depressive Episode, arguing that these may be confounded by the cancer itself. However, this omission may be challenged in terms of the particular somatic symptoms that have been associated with prostate cancer. Therefore, the present study investigated the relative contribution to total depression scores made by the somatic criteria for Major Depressive Episode that were not caused by prostate cancer. Patients and Methods: 491 prostate cancer patients completed the Zung Self-Rating Depression Scale. Data were analysed to compare the predictive power of 5 subsets of depression on patients' total depressive scores. Results: Somatic symptoms were the most powerful predictor of total depression scores, followed by anhedonia and depressed mood, with similar findings for depression clinical status. Emotional symptoms and cognitive confusion were not significant predictors of total depression scores but did predict depression clinical status. Conclusion: Valid and reliable assessment of depression and selection of appropriate treatment options in prostate cancer patients requires consideration of somatic items which match the DSM-IV-TR criteria for Major Depressive Episode.