Past work has shown that parental perceptions of their children’s Internet activity (e.g., hours spent online) does not match their children’s actual Internet involvement; however, no work has examined whether this mismatch is related to youths’ cyberbullying perpetration. Study 1 consisted of 75 parent–child dyads that completed measures to assess youth Internet behavior (including cyberbullying behavior and parental rules regarding Internet behaviors). Results showed that parents, on average, underestimated whether their children cyberbullied others and overestimated parental rule enforcement. Study 2 (N = 165 youth) used a correlational design to examine the relations between youth cyberbullying perpetration and parent Internet rules. Results showed that parental ignorance (how much parents are unaware of their child’s Internet activities) positively correlated with cyberbullying behaviors. Finally, Study 3 (N = 96 youth) used a short-term longitudinal study using the same measure as Study 2 and found that Wave 1 parental ignorance was related to Time 2 cyberbullying perpetration. Overall, results suggest that the extent to which parents are unaware of their child’s online behaviors positively predict cyberbullying perpetration.