In the United Kingdom, new sources of administrative social science data are unfolding rapidly but the quality of these new forms of data for sociological research is yet to be established. We investigate the quality and consistency of the parental occupational information that is officially recorded on administrative birth records by undertaking a comparison with information collected from the same parents in the UK Millennium Cohort Study (MCS). We detect a large amount of missing information in the birth records and a range of inconsistencies. We present an empirical analysis of MCS data using parental social class measures derived both from the birth records and the survey to assess the effects of these discrepancies. We conclude that parental occupational information from administrative birth records should not be assumed, a priori, to be suitable for sociological analyses and that further research should be undertaken into their consistency and accuracy.