The present study uses item response theory (IRT) to establish comparability between the English and Portuguese versions of the Goal Instability Scale (GIS), a measure of generalized motivation. A total of 2,848 American and 679 Portuguese high school students were administered their respective language versions of the GIS. Results showed only minor differences in item performance between language versions, suggesting equivalent measurement of the underlying motivational construct. Implications regarding the interpretation of IRT analyses for intervention purposes, as well as future research, are discussed. (Contains 3 tables and 3 figures.)