The purpose of this paper is to compare the distribution of occupation and rates of occupational mobility in the ATO Longitudinal Information Files (ALife) and the Household, Income and Labour Dynamics in Australia (HILDA) datasets. As tax is not occupation dependent, occupation data from tax records may not be reliable. We find that occupational mobility in the ALife data is less than half that in the nationally representative HILDA data. In contrast, the distribution of occupation and its relationship with most key socio-economic characteristics appear relatively similar across the two datasets. However, occupation evolves differently over time in the two datasets and there are some differences between the sexes.