Background: Increasing attention has been given to subtyping OCD with respect to different clinical profiles, response to drug treatments, comorbidity and age of onset. There are a number of studies looking at predictors of treatment outcome in OCD, but so far not for OCD subtypes. Method: Prediction of outcome after cognitive-behavioural therapy was evaluated in 63 inpatients with early obsessive-compulsive disorder (EOCD ≤ 12 years of age) and 191 patients with late obsessive-compulsive disorder (LOCD > 15 years of age). Results: For EOCD patients factors predicting a good outcome included high motivation and high initial Y-BOCS scores. Factors associated with a bad outcome were higher age at assessment, a longer duration of psychiatric inpatient treatment before assessment and a low level of social functioning (BSS). For LOCD patients living in a stable relationship, high motivation and completing treatment predicted a favourable therapy outcome, while a low level of psychological functioning (BSS) and a longer duration of inpatient psychiatric treatment before assessment were associated with an undesirable therapy outcome. Conclusions: Subtyping OCD patients according to age of onset seems to be a promising avenue towards improving and developing more specified treatment programs.