The effects of postemplacement deformation on originally nonplanar dikes were tested experimentally and compared to field data from the Rainy Lake zone (Ontario, Canada) where irregular fold-like structures are observed. The analyses reveal that two processes are responsible for the irregular dike geometries. First, dikes intrude with varying orientations as they propagate across layers with rheology contrasts, thus developing nonplanar profiles. Second, with postemplacement ductile deformation, dikes that are more competent than the host rocks are folded and refracted in variable amounts, with the amount depending on the initial dike geometry, the heterogeneities in the host, and the regional strain. Deformed dikes and veins are often used as kinematic markers to evaluate regional tectonics, using methods that generally assume that veins had planar walls prior to deformation. The experimental results indicate that caution should be taken when using this approach, and they provide criteria to distinguish between intrusive and deformation structures in intensely deformed areas where distinction between the two is not readily apparent.