Scanning tunneling microscopy of Ni deposited on Au(111) at room temperature reveals strikingly ordered island nucleation. Ni islands grow with spacing 73 along  in rows 140 apart at surface-lattice dislocations induced by the Au(111) herringbone reconstruction. The island arrays are explained by a model in which Ni atoms diffuse on the surface and aggregate at these dislocations. Island size varies by more than the shot-noise limit, suggesting that the initial sticking probability is low when a diffusing atom encounters a dislocation. © 1991 The American Physical Society.