Background The question of whether children should be told of their biological origins is one of the most controversial issues regarding the birth of children through donated eggs, sperm, embryos or surrogacy. Methods In the sixth phase of this longitudinal study when the children were aged 14 years, family relationships and adolescent adjustment were examined in 87 families created through reproductive donation and 54 natural conception families. The quality of family relationships was assessed by standardised interview with mothers and by standardised questionnaires and an observational measure with mothers and adolescents. Adolescent adjustment was assessed using standardised questionnaires. Systematic information on whether and when parents had told children about their biological origins was obtained at earlier phases of the study. Results There were no overall differences between disclosing families and either nondisclosing or natural conception families. However, within the disclosing families, more positive family relationships and higher levels of adolescent wellbeing were found for adolescents who had been told about their biological origins before age 7. Conclusions The earlier children born through reproductive donation are told about their biological origins, the more positive are the outcomes in terms of the quality of family relationships and psychological wellbeing at adolescence.