Alternative splicing is a key molecular event in the gene expression process. It allows for the synthesis of different products from the same gene, and consequently increases the complexity of the proteome encoded by a limited number of genes. Although alterations of alternative splicing are among the myriad of alterations present in tumor cells, increasing evidence indicates that cancer-associated splicing variants play an important role in tumor initiation and progression. Therefore, alternative splicing studies are opening new avenues of research in basic and translational molecular oncology.