Language proficiency policies act as critical gatekeepers for multilingual international students (MIS) who intend to pursue an education at English-medium universities. The current study revisits the question of the predictive validity of a standardized English proficiency exam--International English Language Testing System (IELTS)--in comparison with 10 indices of written syntactic complexity. This study addressed the following questions: (a) Do MIS' overall proficiency and writing subtest scores (IELTS) predict their grade point averages (GPAs) in graduate school? (b) Which syntactic complexity indices in online written production (subordination, coordination, length of production, and degree of phrasal sophistication) predict MIS' GPAs in graduate school? and (c) Which syntactic complexity indices remain predictive of their GPAs when participants' English proficiency scores (overall and/or writing IELTS scores) are added into the model? Participants' IELTS scores, GPAs, and asynchronous discussion postings (224) were analyzed through three linear regressions models. Results confirmed that while IELTS composite and writing subscores do predict academic success of graduate MIS, writing scores are better predictors. After accounting for the contributions of overall and writing subscores, mean length of sentence and T-unit remained significant predictors of academic outcomes, explaining a considerable amount of variance in GPAs, beyond that of IELTS. Equity implications for the admissions of MIS are considered.