Little is known about adult women with attention-deficit/hyperactivity disorder (ADHD); however, available evidence suggests that they experience social impairment. Online social networking websites such as Facebook have become endemic outlets through which emerging adults communicate with peers. No study has examined the peer interactions of emerging adults with childhood histories of ADHD in this developmentally relevant online domain. Participants in the current study were an ethnically diverse sample of 228 women, 140 of whom met diagnostic criteria for ADHD in childhood and 88 who composed a matched comparison sample. These women were assessed at 3 time points spanning 10 years (mean age = 9.6 at Wave 1, 14.1 at Wave 2, 19.6 at Wave 3). After statistical control of demographic covariates and comorbidities, childhood ADHD diagnosis predicted, by emerging adulthood, a greater stated preference for online social communication and a greater tendency to have used online methods to interact with strangers. A childhood diagnosis of ADHD also predicted observations of fewer Facebook friends and less closeness and support from Facebook friends in emerging adulthood. These associations were mediated by a composite of face-to-face peer relationship impairment during childhood and adolescence. Intriguingly, women with persistent diagnoses of ADHD from childhood to emerging adulthood differed from women with consistent comparison status in their online social communication; women with intermittent diagnoses of ADHD had scores intermediate between the other 2 groups. Results are discussed within the context of understanding the social relationships of women with childhood histories of ADHD.