Advances in scientific techniques have provided researchers with exceptional new opportunities to identify and monitor changes between different cancer types, during different stages of progression, between individual tumor cells and in the surrounding stroma. The wealth of information that can be obtained from new scientific techniques places additional requirements on the conventional cancer models. New models that could be used to rapidly access the (potential) functional importance of newly identified (epi)genetic and proteomic changes and test the efficacy on emerging (combinatorial) therapies are desperately required. The distinctive characteristics of zebrafish are progressively being applied to create more relevant models of human diseases. Zebrafish embryos provide a powerful tool to develop functional cancer models. This is a tool that can be used from drug discovery and development to assessment of drug toxicity. This review will summarise the use of zebrafish xenograft models to study human cancers, and discuss the benefits and limitations of these models.