A recently proposed new mechanism of thin film dewetting (Wensink, K. D.; Jerome, B. Langmuir 2002, 18, 413) is revisited, and conditions are established under which rupture of a thin film can be engendered by the density variations caused by changes in its local thickness. An increase in the density with the increasing film thickness can actually stabilize a thermodynamically unstable film. In the opposite case of decrease in the density with increasing film thickness, a thermodynamically stable thin film can be destabilized. Nonlinear simulations confirm the validity of the linear stability analysis. Morphological characteristics of this novel density variation induced instability closely resemble the well-known spinodal dewetting at constant density.