Alternative pre-mRNA splicing is a key molecular event that allows for protein diversity. Through this process, a single gene increases its coding capacity by expressing several related proteins with diverse and even antagonistic functions. Aberrant splicing has been found to be associated with various diseases, including cancer. Mutations in splicing regulatory elements within the nucleotide sequence and alterations in the cellular-splicing-regulatory machinery both result in changes in the splicing pattern of many cancer-related genes. The analysis of cancer-specific alternative splicing and its molecular consequences is promising. In this review we summarise the current knowledge on the mechanisms governing abnormal alternative splicing in cancer and the biological consequences associated with the alteration of splicing in some relevant cancer-related genes. The use of alternative splicing as a potential source for new diagnostic, prognostic, predictive, and therapeutic tools is also discussed.