We used nest boxes to study communal nesting and breeding habits of Glaucomys volans (Southern Flying Squirrel) at high elevations over a wide geographic range in western Virginia from 1985 to 1996. Of 320 occupied nest boxes, 19.1% contained litters, 20.3% contained solitary adults, 45.9% had adult aggregations, and 14.7% contained individuals or aggregations of unknown age. Aggregation size ranged from 2–12 individuals. Group size appeared larger during winter months, while the greatest number of aggregations peaked between June and August; however, neither trend was significant. Females were significantly more numerous than males in mixed-age aggregations, while males were significantly more abundant than females in adult aggregations. The breeding season, from first conception to last weaning, lasted 46–48 weeks, from the fourth week of January through the second week of December. Two distinct parturition peaks were evident in late March to mid-April and mid-August to mid-September. Our data support the hypothesis that reproductive activity of Southern Flying Squirrels varies by latitude and is primarily determined by photoperiod length, at least in temperate areas.