Regularities such as symmetry and repetition can facilitate visual object processing. Nevertheless, the interaction between type of regularity and objectness is not very clear. Previous research indicated that symmetric contours that appear to belong to one object may have an advantage over symmetric contours that appear to belong to two objects; and vice versa for repetition. However, both symmetry and repetition influence the perceptual grouping of elements in an image and therefore also the perceived number of objects (i.e., the objectness of visual elements). Here, we present three experiments in which projections of 3-D objects, as well as stereoscopically presented images, were used to more clearly separate one-object from two-object displays perceptually. In these experiments, participants had to indicate whether a regularity (symmetry or repetition, administered in separate blocks) was present or not. Overall, it was found that symmetry detection was easier for one-object displays than for two-object displays, and vice versa for repetition. More importantly, this result was found irrespective of the configuration of the presented elements. We conclude that this interaction between type of regularity and number of objects in fact depends on the objectness of the stimuli.