In previous studies of homework in core academic subjects, positive student attitudes toward homework were linked to higher achievement, whereas time spent on homework showed an inconsistent relationship with achievement. This study examined the generalizability of these findings to foreign language learning by analyzing 2,342 adult students' attitudes toward assigned homework, time spent on assigned homework, and achievement outcomes in a variety of foreign language courses. Student ratings of the relevance of homework, the usefulness of feedback provided on homework, and the fairness of homework grading were positively correlated with teacher-assigned grades and standardized proficiency test scores in listening, reading, and speaking. Reported time spent on homework, however, was negatively correlated with these measures. In hierarchical regression analyses, all homework-related variables emerged as significant predictors of outcomes after controlling for potential covariates such as language learning aptitude, demographic variables, and affective factors. Thus, these results provide evidence that language course outcomes are positively associated with attitudes toward homework but negatively associated with time spent on homework. Possible interpretations of these findings are discussed. We suggest that the negative association follows in part from the opportunity cost of time spent on assigned homework, which decreases time spent on individualized study that may be more beneficial for improving language course outcomes.