Accumulating evidence suggests that early adversity is linked to methylation of the glucocorticoid receptor (GR) gene, "NR3C1," which is a key regulator of the hypothalamic-pituitary-adrenal axis. Yet no prior work has considered the contribution of methylation of "NR3C1" to emerging behavior problems and psychopathology in childhood. This study examined the links between methylation of "NR3C1" and behavior problems in preschoolers. Data were drawn from a sample of preschoolers with early adversity (n = 171). Children ranged in age from 3 to 5 years, were racially and ethnically diverse, and nearly all qualified for public assistance. Seventy-one children had child welfare documentation of moderate to severe maltreatment in the past 6 months. Structured record review and interviews in the home were used to assess early adversity. Parents reported on child internalizing and externalizing behavior problems. Methylation of "NR3C1" at exons 1[subscript D], 1[subscript F], and 1[subscript H] were measured via sodium bisulfite pyrosequencing from saliva DNA. Methylation of "NR3C1" at exons 1[subscript D] and 1[subscript F] was positively associated with internalizing (r = 0.21, p < 0.01 and r = 0.23, p < 0.01, respectively), but not externalizing, behavior problems. Furthermore, "NR3C1" methylation mediated effects of early adversity on internalizing behavior problems. These results suggest that methylation of "NR3C1" contributes to psychopathology in young children, and "NR3C1" methylation from saliva DNA is salient to behavioral outcomes.