This review focuses on the possibilities of scintigraphy in the diagnosis, staging and therapy outcome of tumors in animals and man. A comparison is made with the current state of the art in human oncology and veterinary medicine. An overview is given concerning the working mechanism of the different commercially available radiopharmaceuticals, with emphasis on their specific use, depending on the clinical requests. Recent developments concerning new generations of radiopharmaceuticals which have the potential to offer more specificity and sensitivity, especially in the domain of therapy prediction and outcome, are mentioned. Despite its limitations, due for the most part to the limited system resolution and the lack of specificity of the currently available radiotracers, this modality offers additional diagnostic information compared to the conventional anatomical imaging techniques.