We report what is believed to be the first observation of lasing of an optically pumped thin CdS film formed by laser ablation on glass. Laser action is observed at room temperature, and the emission peak is at 501 nm. X-ray diffraction shows that the polycrystalline films are of wurtzite structure and have (002) preferred orientation. Fabry-Perot laser modes are spaced 16 nm apart, indicating a cavity length of 2.9 μm. The cavity is formed by consistently self-formed microcavities within the hexagonal lattice.