Cancer initiation and progression has been linked to oxidative stress, a condition in which the balance between production and disposal of reactive oxygen or nitrogen species is altered. Oxidative stress has several protumorigenic effects, such as increasing DNA mutation rate or inducing DNA damage, genome instability and cell proliferation. Conversely, oxidative stress also exerts antitumorigenic actions, and it is has been linked to senescence and apoptosis, two major mechanisms that counteract tumor development. In this review, recent findings that relate oxidative stress to cancer-associated conditions, such as chronic inflammation, steroid hormone signaling and altered chromosome segregation, are highlighted, and how these studies may identify new targets for the development of drugs and strategies for cancer prevention and cure is discussed.