This study aimed to determine how alexithymia affects the perception of illness in patients with cancer. This was a descriptive study conducted at the Ataturk University Health, Research and Practice Hospital and the Erzurum Regional Training and Research Hospital's Medical Oncology Clinic and Chemotherapy Unit. The study data were collected between July 2013 and January 2014. In total, data were collected from 283 patients with cancer. The data were collected using questionnaires enquiring about demographic and medical information: the IPQ and TAS-20. The study concluded that 50.5% of the participating patients had alexithymia. It was found that the alexithymic patients with cancer perceived the negative outcomes of their illness more strongly, and their negative feelings about the illness were more intense. This study suggests that further research should be carried out on alexithymia in patients with cancer and that their positive beliefs about the illness could be enhanced using psychosocial interventions.