A 48-year-old woman with exanthema, pruritus and eosinophilia was found upon further examination to have a small-cell bronchus carcinoma; after chemotherapy and radiotherapy there was an almost complete response and the skin symptoms disappeared. A 70-year-old man who was recently treated due to primary malignant fibrous histiocytoma associated with eosinophilia became cachectic and anaemic. He was found to have a metastased leiomyosarcoma and died shortly afterwards. Worldwide the most common cause of eosinophilia is a parasitic infection, whereas in Western Europe the most common causes are allergic reactions and medicine use. Paraneoplastic symptoms are present in 7-10% of adults with cancer. However, the frequency of eosinophilia as a paraneoplastic phenomenon is unknown. It is important to recognise this phenomenon of paraneoplastic eosinophilia for the timely diagnosis and treatment of the underlying disease.