We present an N-body simulation of a galaxy with a long-lived two-armed spiral pattern. The model consists of a static bulge and halo and an active disk of 60,000 particles. The disk contains 41 % of the total mass of the system. The resulting rotation curve has a steeply rising central part and is falling at larger radii. Half of the disk particles represents an old stellar population, half of them gas clouds that can collide inelastically with each other.