Stimulated emission by optical pumping of solid-state organic materials has been well known since the late 1960s following the first demonstrations of laser action in dye-doped gels and molecular crystals(1-4). Interest in this field has been revived by the demonstration of efficient, long-lived and intense electroluminescence in both polymeric(5) and small-molecular-weight(6) organic thin films, which indicates the possibility of laser action in these materials. Several recent studies of optically pumped polymers have reported emission phenomena suggestive of laser action(7-9). Here we present clear evidence for laser action from optically pumped, vacuum-deposited thin films of organic molecules, in both slab-waveguide and double-heterostructure configurations. This realization of laser action in conducting organic thin films should open the way to the development of a new class of electrically pumped laser diodes.