Androgens are known to exert their effects via genomic signalling, which involves intracellular androgen receptors that modulate gene expression on steroid binding. Whereas non-classical estrogen effects are well established, it is only recently that non-classical, rapid, membrane-initiated testosterone actions have received attention. Non-classical effects of testosterone have now been demonstrated convincingly in several tissues, in particular in the reproductive, cardiovascular, immune and musculoskeletal systems. There is evidence for the participation of the classical intracellular androgen receptor and for involvement of novel, membrane-associated androgen receptors in the non-classical actions of testosterone. Here we discuss evidence for rapid testosterone actions, which have clinical implications in fertility, cardiovascular disease and the treatment of prostate cancer.