We examined the relationship between being bullied during childhood and activity of the hypothalamic–pituitary–adrenal (HPA) axis as assessed through repeated measures of salivary cortisol. A non-clinical sample of 154 (74 boys) predominantly Caucasian middle-class 12-year-olds each provided detailed information about their experiences with bullying and six saliva samples were standardized across time and day. Children with a history of child maltreatment, diagnosed psychiatric illness, foster care placement, medication use (psychotropic and oral contraception) and aggression directed toward peers and/or family members were excluded. Using multilevel regression and applying orthogonal polynomial contrasts to model the observed circadian pattern in the data, we found that occasional and frequent verbal peer victimization was associated with hyposecretion of cortisol when controlling for sex, pubertal status, age, depression and anxiety. This relation, however, was moderated by sex. For boys, occasional exposure was associated with higher cortisol levels, whereas for girls exposure was associated with lower cortisol levels. The present study highlights the need to consider the plight of peer-victimized children seriously, as it is associated with alterations to the HPA axis that affect males and females differently, and likely diminishes a person's ability to cope with stress, possibly placing them at risk for psychopathology and ill health. Aggr. Behav. 34:294–305, 2008. © 2007 Wiley-Liss, Inc.