Irrational or maladaptive thinking patterns of child molesters are widely acknowledged as an important variable in the initiation and maintenance of sexual offending behaviour. However, there lacks an adequate descriptive model of child molester's cognitions from a broad, empirically grounded approach. The aim of this study was to develop a classification model which encapsulates the cognitions used by offenders when describing or rationalising their offences and offending history. Offence descriptions were obtained from twenty incarcerated male child sexual offenders undergoing assessment for a sexual offending treatment program. A data-driven approach, grounded theory, was taken in the qualitative analysis of these offence accounts. The resulting model, The Model of Dysfunctional Cognitions of Child Molesters, comprises of four levels; Offence Chain; Cognitive Operations; Cognitive Content; and Meta-Variables, on which cognition is classified. The model differentiates content from process, describing the content of sexual offenders' cognitions, the processes involved in relaying offence information and the general processing style of sexual offenders. In order to determine cross validity and reliability, the model was applied to the offence descriptions of a sample of 25 incarcerated child molesters also undergoing pre­ treatment assessment. Results suggest that the model has provisional validity and adequate interrater reliability. Components of the model are discussed in comparison to existing classification systems and theoretical research. Clinical utility of the model as an assessment instrument, and as a methodological tool for future research, are discussed.