A significant proportion of cancer patients experience psychiatric morbidity. Potential predictors of psychiatric morbidity include patient disease-related factors and factors relating to the patient's environment. The aim of this study was to investigate the prevalence of psychiatric morbidity and the relationship between the clinical or personal factors, especially psychiatric morbidity, and awareness of cancer diagnosis among a group of Turkish cancer patients. A total of 117 cancer patients were assessed using the Structured Clinical Interview for DSM-IV (SCID), the Hospital and Anxiety Depression Scale (HADS) and the General Health Questionnaire (GHQ). Of these patients, 30% had a psychiatric diagnosis. Adjustment disorders comprised most of the psychiatric diagnoses. Awareness of the diagnosis of cancer, history of previous psychiatric disorders, pain and stress factors were correlated with psychiatric morbidity. Of the 117 patients, 64 (54.7%) were unaware of the diagnosis of cancer. Most of the patients (67.9%) who were considered to be aware of the cancer diagnosis stated that they had guessed their illness from the treatment process or drug adverse effects. Psychiatric morbidity was significantly higher in the patients who knew that they had a cancer diagnosis (P=0.03). These findings suggest that the awareness of cancer diagnosis is related to the presence of psychiatric morbidity. In particular, the understanding of the diagnosis indirectly may be stressful to the patient because it arouses suspicion about the cancer and treatment, and consequently can lead to psychiatric disturbance. In Turkey honest disclosure of the true diagnosis is still not common for cancer patients and it seems to be essential to improve this situation.