 Depression can be challenging to diagnose in patients with cancer. A spectrum of depressive symptoms can be seen, ranging from appropriate sadness in response to a life threatening diagnosis, to a major depressive episode. The diagnosis is confounded by the symptoms brought on by the cancer and its treatment, such as fatigue, insomnia, anorexia, and pain. Medications commonly used in cancer patients such as narcotics, benzodiazepines, antihistamines, steroids, antibiotics, chemotherapy, and endocrine therapy can all lead to side effects that further confuse the picture. However, while challenging, evidence does suggest that a valid diagnosis of depression can be made in this patient population. 