The rate and predictors of parental detection of youth self-harm behavior and relationship with help-seeking were examined in 7,036 parent-child dyads from the 1999 and 2004 surveys of Mental Health of Children and Young People in Great Britain. Youth self-harm behavior was reported by 463 (6.6%) children and adolescents but only 190 (2.7%) of the parents (kappa = 0.30). Reports were more accurate if parents were from majority White ethnicity, were mothers of girls, experienced psychological distress themselves, or if children were older or had emotional/behavioral problems. Parental detection of youth self-harm was associated with increased likelihood of professional help-seeking.