Queen polymorphism , the occurrence of several morphologically distinct forms of reproductive females within one species, has been reported in several Ponerinae, and in some mostly socially parasitic Formicinae and Myrmicinae. We report here the first record of a queen polymorphism in a non-parasitic leptothoracine species. Dealate gynomorhic as well as intermorphic and nearly ergatomorphic specimens are found to be the reproductive queens in several populations of this species along St. Lawrence River, Quebec, Canada. The species is functionally monogynous, having only one reproductive female in each colony, and often one o r several inseminated but not egg-laying potential queens. Intermorphs may have identical offspring, or produce both intermorphs and gynomorphs as young potential queens. A genetical origin of this queen polymorphism, as in Harpagoxenus sublaevis, is suggested. The species is related to Leptothorax muscorum (Nyl.), but not yet definitely identified. The queen polymorphism is described, the known range of the phenomenon and preliminary results of breeding experiments are recorded.