We examined the associations between attachment-related symptoms (symptoms of reactive attachment disorder (RAD), symptoms of disinhibited social engagement disorder (DSED), and clinging) and later psychological problems among international adoptees. The study population comprised internationally adopted children (591 boys and 768 girls, 6-15 years) from the ongoing Finnish Adoption (FinAdo) study. Data were gathered with self-administered questionnaires both from adoptive parents and from adoptees aged over 9 years. Attachment-related symptoms were measured using of a short (8-item) questionnaire and later behavioral/emotional problems were assessed using the Child Behavior Checklist (CBCL) and the Five to Fifteen (FTF) scale for attention-deficit/hyperactivity disorder (ADHD) symptoms. RAD and DSED symptom subscales were associated with an increased risk of emotional and behavioral problems and ADHD. Especially the mixed type of attachment-related symptoms was strongly associated with later emotional and behavioral problems.