BACKGROUND: The mode of questionnaire administration may affect the estimates and applicability of oral health-related quality of life indicators. The aim of this study was to compare psychometrically the self-administered Child-OIDP index with the original interviewer-administered instrument. METHODS: This was a cross-sectional study of 144 consecutive children aged 9-16 years referred to orthodontic clinics in Bedfordshire. To compare the two administration modes of the Child-OIDP, the sample was randomly split in two groups. The two groups were analysed in terms of baseline characteristics, self-perceived measures (self-rated oral health, self-perceived need for braces, happiness with dental appearance, frequency of thinking about dental appearance), Child-OIDP performance scores and overall score and psychometric properties (criterion validity and internal reliability). RESULTS: No significant difference between the two groups was found in relation to their sociodemographic profile and self-perceived measures. The self- and interviewer-administered Child-OIDP had identical mean scores and did not differ in recording any of the eight performances (p > or = 0.206). For criterion validity, the correlation coefficients of the Child-OIDP with self-perceived measures were not different between the two modes of administration (p > or = 0.118). Furthermore, the Cronbach's alpha values of the two groups were similar (p = 0.466). CONCLUSION: This study demonstrated that the self-administered Child-OIDP performed the same as the original interviewer-administered mode, while at the same time reducing administration burden. This provides support for the use of the self-administered Child-OIDP. Further studies should focus on a more comprehensive psychometric evaluation.