The structure and dynamics of a single molecule of the nonionic surfactant polysorbate 80 (POE (20) sorbitan monooleate; Tween 80 (R)) as well as a micelle comprising sixty molecules of polysorbate 80 in water have been investigated by molecular dynamics simulation. In its free state in water the polysorbate 80 molecule samples almost its entire conformational space. The micelle structure is compact and exhibits a prolate ellipsoid shape, with the surface being dominated by the polar terminal groups of the POE chains. The radius of gyration of the micelle was 26.2 angstrom. The physical radius, determined from both the radius of gyration and atomic density, was about 35 angstrom. The estimated diffusion constants for the free molecule (1.8 x 10(-6) cm(2) s(-1)) and the micelle (1.8 x 10(-7) cm(2) s(-1)) were found to be remarkably close to the respective experimental values. The lateral diffusion of the molecules on the micelle surface was estimated to be 1.7 x 10(-7) cm(2) s(-1), which confirms the highly dynamic nature of the micelle structure.