As the number of veterinary patients, especially dogs, suffering from malignant disease grows and owners demand human-care quality for their pets, research on the identification and treatment of malignant diseases in veterinary medicine is growing in importance. Malignant diseases are not only connected with direct thickening and ingrowth of tissue, but also with the paraneoplastic syndromes, i.e. remote effects of tumors. In general, they are caused by hormones, peptides, and cytokines secreted by tumors or immune cross-reactivity between malignant and normal tissues. Paraneoplastic syndromes can be divided into several well defined categories, the most important being: hematological, endocrine, mucocutaneous, gastrointestinal, renal and neurological paraneoplastic syndrome as well as hypertrophic osteopathy and fever. All these syndromes significantly affect the presentation, clinical course, and available treatment for primary malignancies they are related to. Recent diagnostic and therapeutic advances in identification and treatment of paraneoplastic disorders have had a great impact on clinical outcome of malignant diseases, ranging from earlier cancer diagnosis, to improved quality of life and extended life expectancy.