Statins have been successfully used in patients with hypercholesterolemia and cardiovascular diseases, but there is increasing evidence that they exert effects by much exceeding the lowering of cholesterol levels. Statins have antiatherosclerotic, antiinflammatory, antioxidant, immunomodulatory and antithrombotic effects. These "pleiotropic" effects stem from their inhibition of prenylation of the small GTP-binding proteins Ras and Rho, and to the disruption, or depletion, of cholesterol rich membrane micro-domains (membrane rafts). Through these pathways statins modulate immune responses by altering cytokine levels and by affecting the function of cells involved in both innate and adaptive responses. Anti-inflammatory and immunosuppressory properties of statins provide the rationale for their potential application in conditions in which the inflammation and immune response represent key pathogenic mechanisms, such as antiphospholipid syndrome, rheumatoid arthritis and systemic lupus erythematosus. Reduction of atherosclerosis progression in autoimmunity is also a very important effect. Statins pathways of action in systemic autoimmune diseases, and their potential therapeutic use are discussed in this review. The inhibition of mevalonate pathway by statins impairs modification of Ras and Rho GTPases, which play key roles in signaling pathways related to tumor formation, metastasis and cell death. There is experimental and clinical evidence that statins may improve the therapeutic outcome of anticancer drugs. Thus, this review will also discuss recent insights into the molecular mechanisms underlying the anticancer effects of statins and their assessment as promising candidates for inclusion into current therapeutic regimens for the treatment of malignant diseases.