Using high-aspect-ratio nanostructures fabricated via two-photon laser-scanning lithography, we examine the deformation of elastomeric stamps used in soft nanolithography and the fidelity of patterns and replicas made using these stamps. Two-photon laser-scanning lithography enables us to systematically regulate the aspect ratio and pattern density of the nanostructures by varying laser-scanning parameters such as the intensity of the laser beam, the scanning speed, the focal depth inside the resist, and the scanning-line spacing. Two commercially available stamp/mold materials with different moduli have been investigated. We find that the pattern-transfer fidelity is strongly affected by the pattern density. In addition, we demonstrate that true three-dimensional structures can be successfully replicated because of the flexible nature of elastomeric poly(dimethylsiloxane).