Purpose: Disruptive behavior disorders (DBD), including oppositional defiant disorder (ODD) and conduct disorder (CD), are some of the most common psychiatric conditions in childhood. Despite this, there has been limited research on DBDs. We examined the incidence, comorbidity and gender differences of DBDs diagnosed by specialist services.

Method: This was a nationwide register study of 570,815 children and adolescents born in 1996-2005. The 7050 individuals diagnosed with DBD by specialist healthcare services were matched to 26,804 controls.

Results: By the age of 15, the cumulative incidence of diagnosed DBDs was 3.5% for boys and 1.4% for girls. The yearly incidence rate increased for girls after 13 years of age, while the incidence for boys was relatively stable between 8 and 15 years of age. When we compared subjects born between 1996-1998 and 1999-2001, we found that by the age of 12, the cumulative incidence per 100 people had increased from 0.56 to 0.68 among girls and from 2.3 to 2.6 among boys. This indicated a minor increase in treated incidence. The parents of children diagnosed with DBDs had lower educational levels than the parents of controls. Children with DBD were also more likely to have been diagnosed with other psychiatric disorders.

Conclusion: Although DBDs were 3.5 times more common among boys during the whole follow-up period, the yearly incidence during adolescence was fairly similar between boys and girls. DBD existed alongside various psychiatric disorders at a relatively young age and only a minor increase in treated incidence was found during childhood.Keywords: Co-morbidity; Conduct disorder; Disruptive behavior disorder; Oppositional defiant disorder; Register-based study.