Female mating frequency has important implications for the evolution and maintenance of sociality in social insects. We examined mating frequencies of queens in a social wasp, Dolichovespula arenaria (Vespidae, Vespinae). Colonies of D. arenaria were collected in the subalpine zone of the Front Range of the Colorado Rocky Mountains in 2002 and 2003. Worker, queen, and male genotypes were analyzed using DNA microsatellites. The hypothesis of single mating by queens was supported in five of the seven colonies. Data from the other two colonies supported two and three matings, with effective paternity of 1.48 and 1.91, respectively. Worker relatedness ranged from 0.57 to 0.83 within each of the seven colonies sampled with a mean relatedness of 0.77+ 0.09. Four colonies contained males; these were assigned as worker or queen progeny using both the exclusion and maximum likelihood methods; each method yielded similar results. In two of these colonies, all males were likely progeny of the queen. In the other two colonies workers produced 8 and 14% of the males. Overall, 91.5% of the males in the population were likely progeny of the queen. These patterns are consistent with published studies of vespine wasps.