Research has shown that general vocabulary knowledge (e.g., Milton & Treffers-Daller, 2013), academic vocabulary knowledge (e.g., Townsend et al., 2012) and general intelligence (e.g., Laidra et al., 2007) are good predictors of academic achievement. While the effect of these factors has mostly been examined separately, Townsend et al. (2012) have tried to model the contribution of general and academic vocabulary to academic achievement and find academic vocabulary knowledge adds only marginally to the predictive ability of general vocabulary knowledge. This study, therefore, examines further factors as part of a more extensive predictive model of academic performance, including L1 vocabulary knowledge, L2 general and academic vocabulary knowledge, and intelligence (IQ) as predictors of overall academic achievement among learners of EFL. Performance on these measures was correlated with Grade Point Average (GPA) as a measure of academic achievement for undergraduate Arabic L1 users (N = 96). The results show positive significant correlations between all the measures and academic achievement. However, academic vocabulary knowledge shows the strongest correlation (r = 0.72) suggesting that the pedagogical use of this list remains important. To further explore the data, multiple regression and factor analyses were performed. The results show that academic and general vocabulary knowledge combined can explain about 56% of the variance in students' GPAs. The findings, thus, suggest that, in addition to L1 and L2 vocabulary size, and IQ, knowledge of academic vocabulary is an important factor that explains an additional variance in learners' academic achievement.