Reproductive success of red-cockaded woodpeckers (Picoides borealis) appears to be reduced when even a single cavity in a cluster of woodpecker cavities is occupied by a southern flying squirrel (Glaucomys volans). One potential technique for reducing flying squirrel use of woodpecker cavities is the addition of nest boxes to clusters. In this study we evaluated the effects of nest boxes and red-cockaded woodpecker presence (activity) on flying squirrel use of cavities at the Joseph W. Jones Ecological Research Center in Newton, Georgia from 26 September 2002 until 26 June 2003. The interaction between presence of nest boxes and woodpecker activity significantly affected success (proportion of time no flying squirrels occupied any cavities in a cluster; F1,16 = 5.10, P = 0.04). Success was higher in active clusters with nest boxes (95%) than active clusters without nest boxes (83%) but was similar in inactive clusters (success with and without nest boxes = 78%). The proportion of cavities usurped by squirrels cluster−1 month−1 was higher for inactive clusters (0.07) than for active clusters (0.03; F1,16 = 6.59, P = 0.02). The number of usurped nest boxes per cluster was higher for active clusters (5.67) than inactive clusters (2.71; F1,8 = 4.56, P = 0.07). Our results indicate that nest box addition coupled with flying squirrel removal may reduce flying squirrel use of cavities, especially when cavities occur in clusters containing red-cockaded woodpeckers.