The clinical practice of child and adolescent psychiatry includes encounters with disorders not particular to childhood and adolescence, but seen in adulthood as well. For example, among the neurotic disorders, obsessive-compulsive disorder can be seen from around 3 years of age, with rapid rise in prevalence from around age 10. Increase is also seen in cases of anorexia nervosa from around age 11. This report examines the association between disorders in childhood and adolescence, in comparison to that in adulthood, with focus on obsessive-compulsive disorder. To start with, the characteristics of childhood onset cases with onset under age 7 were reviewed, revealing a relatively large proportion of subjects with experience of separation anxiety. Analyses revealed the possibility of anticipating obsessional tendencies in the parents of such subjects. Further clarification of the features of such early onset cases is hoped for in future. Next, we conducted a literature review comparing the characteristics of child and adolescent obsessive-compulsive disorder with that in adulthood. It has been determined that obsessive-compulsive symptoms in childhood and adolescence have a relatively unyielding 4-factor construct that persists through life, namely: 1) symmetry factor, 2) forbidden thoughts factor, 3) cleaning factor, and 4) hoarding factor. Of these, children with primary symptoms of hoarding are said to have poorer long-term diagnoses than children with other symptoms. Another point of note is the presence of large disparity regarding the prognosis of cases with concomitant tics. While the prognosis of childhood-obsessive compulsive disorder is generally favorable in many reports, the need for caution has also been noted regarding the possibility of transition on to schizophrenia in more than just a few cases.