The void formation energies in simple metals are calculated in the stabilized jellium model. The total energies of stabilized jellium spheres mimicking small clusters of simple metals are determined. The electronic structures are solved in both cases self-consistently within the local density approximation for electron exchange and correlation. The planar surface energies and the curvature energies are extracted from the results. The stabilized jellium model is shown to give a physically meaningful description of planar surfaces as well as surfaces with positive or negative curvature. The results for voids and clusters are discussed using the so-called liquid drop model and its generalization. They are used to estimate edge and step formation energies.