Many cellular processes have been identified in which phosphatidylinositol 3-kinase has a key regulatory function. As an oncogene, it is also involved in the development of cancer. The transformation and progression of normal cells towards an advanced stage tumor and/or towards metastatic lesions involves a complex series of events, including genetic alterations, leading to aberrant cell cycle progression, altered adhesion and motility characteristics, inhibition of apoptosis and induction of angiogenesis. This review highlights the processes involved in the pathogenesis of cancer in which phosphatidylinositol 3-kinase is involved and provides an overview of the possible mechanisms by which the enzyme exerts its oncogenic action.