The Modern Language Aptitude Test (MLAT) was part of a project examining biographical, motivational, attitudinal, personality, and cognitive aptitude variables in 1,000 adult students preparing at the Foreign Service Institute for overseas assignments, with various subsamples completing different instruments. Data were analyzed using correlation, ANOVA, chi-square, and mulitple regression as appropriate to the data and research questions. The MLAT proved the best of the available predictors of language learning success. As part of an effort to expand the concept of language learning aptitude beyond the strictly cognitive, this study related the MLAT not only to end-of-training proficiency outcomes, but also to personality disposition, using both overall correlational data and information on extremely strong and weak learners. The MLAT has been found about equivalent in its current predictive power (based on correlation) to the time it was developed. In addition, it was found to be especially powerful at the extremes of performance as measured by speaking proficiency. Links between high MLAT scores and various other individual characteristics, including personality variables, emerged. Qualitative findings from use of MLAT part scores in student counseling also suggest utility for this well-established instrument beyond prediction of learning success. (Contains 45 references.) (Author/MSE)