This article reports on two studies conducted at the same university, one investigating the link between ESL scores on an advanced ESL test and the grade point average (GPA) obtained over two semesters and the other investigating the link between French second language (FSL) scores on an advanced L2 test and both the number of courses failed and the first semester GPA. Graham's (1987) review of the literature pointed out the problems associated with research that attempts to delineate the relationship between language proficiency and academic performance, including the nature of the measures used to define L2 proficiency; the definition of academic success, especially when the GPA reported may be based on unequal numbers of courses or on dissimilar courses; and the possible influence of other variables in determining academic success. Language proficiency in our two studies consisted of measures of listening (FSL only), reading comprehension, and writing ability based on communicative principles previously validated in other work. The participants in the ESL study were 34 overseas Chinese students who had all participated in a pre-study English for Academic Purposes (EAP) program and were subsequently enrolled in a Master of Business Administration (MBA) program, where they were tracked for 18 months. Those in the French study were Canadian L1 and L2 French speakers (N = 100, N = 36) enrolled in a three-year program in civil law. In both programs, all students took the same courses. In the ESL study, other data were obtained from interviews with professors and students, a questionnaire on reading practices, and final exam marks. In the FSL study, comparisons were made between L1 and L2 profiles on the measures outlined above and the students' incoming college grades. From these data it has been possible to provide more complete answers regarding the relationship of language proficiency to academic success than was possible in much previous work.