In this study, we examine the degree of construct comparability and possible sources of incomparability of the English and French versions of the Programme for International Student Assessment (PISA) 2003 problem-solving measure administered in Canada. Several approaches were used to examine construct comparability at the test- (examination of test data structure, reliability comparisons and test characteristic curves) and item-levels (differential item functioning, item parameter correlations, and linguistic comparisons). Results from the test-level analyses indicate that the two language versions of PISA are highly similar as shown by similarity of internal consistency coefficients, test data structure (same number of factors and item factor loadings) and test characteristic curves for the two language versions of the tests. However, results of item-level analyses reveal several differences between the two language versions as shown by large proportions of items displaying differential item functioning, differences in item parameter correlations (discrimination parameters) and number of items found to contain linguistic differences. (Contains 2 tables and 3 figures.)