Research shows that meaning-focused reading offers opportunities for incidental grammar acquisition. However, the number of such studies remains limited and none have examined the role of both in-text encounters with grammar structures and reading comprehension in this learning. The present study filled these gaps. Employing a between-group, pretest-posttest-delayed-posttest experiment, this study examined to what extent four groups of English-as-a-Foreign-Language adult learners (n = 132) in Vietnam learnt two specific grammar structures through meaning-focused reading in which they encountered these structures four, six, eight, or ten times. A control group (n = 30) was also added to this experiment to gauge test-taking effects. Grammar gain was measured by a self-report grammar-knowledge scale, while content comprehension by a topic-matching task. All treatment groups were found to make sizeable grammar gains, especially after six encounters with the structures. Reading comprehension could also predict the learning gains. These findings offer various useful pedagogical implications.