Nitric oxide (NO) is a second messenger with diverse roles in the cardiovascular system, such as inhibiting thrombosis and limiting vascular inflammation. One mechanism by which NO modulates such disparate physiological processes is by regulating protein trafficking within cells. NO inhibits exocytosis of endothelial granules which would otherwise trigger inflammation. NO also blocks platelet secretion of granules that would otherwise activate thrombosis. NO decreases granule trafficking from the Golgi to the plasma membrane by targeting a key component of the exocytic machinery, N-ethylmaleimide sensitive factor (NSF). In contrast to its inhibitory effects on exocytosis, NO accelerates endocytosis. S-nitrosylation of dynamin increases its ability to hydrolyze GTP, assemble in oligomers around a nascent vesicle, and cleave the endocytic vesicle free from the plasma membrane. NO regulation of vesicle trafficking is a molecular mechanism that explains some of the cardiovascular effects of NO, and may be of broad physiological significance.