The plastic deformation of a pentagonal silver nanowire is studied by nanoindentation using an atomic force microscope (AFM). AFM images of the residual indent reveal the formation of a neck and surface atomic steps. To study the microscopic deformation mechanism, the indentation force-depth curve is converted to an indentation stress-strain curve and compared to the tensile stress-strain curves predicted by the atomistic simulations of pentagonal silver nanowires. The indentation stress-strain curve exhibits a series of yielding events, attributed to the nucleation and movement of dislocations. The maximum stress measured during nanoindentation (2 GPa) is comparable to the tensile yield strength predicted by atomistic simulations. © 2008 The American Physical Society.