This paper uses A-level Information System (ALIS) data to quantify the determinants of the choice between Economics and Business Studies at A-level. These subjects are often perceived as close curriculum options and possible substitutes in the UK. Subject choice is modelled using an underlying latent variable approach. On the basis of a series of counterfactual exercises an overall average grade differential, a measure of their comparative difficulty, is estimated to be 1.3 (old) UCAS points, equivalent to approximately two-thirds of a letter grade, in favour of Business Studies.The estimating equation suggests that a unit increase in the grade differential increases the probability of selecting Business Studies over Economics by approximately 12 percentage points.There is evidence that females are less likely to choose Economics over Business Studies and the more able students, in terms of their average GCSE score and mathematical ability, are more likely to select Economics.There is also some evidence of parental background characteristics and ethnicity exerting significant effects on the choice between these two subjects.