This study compared the effects of students’ dictionary use with teacher’s instruction on vocabulary tests performance and perceptions among Iranian university students. Seventy participants were divided into two groups, with and without the presence of a teacher. In four consecutive weeks and in four different treatments, Group A received vocabulary lists and dictionaries for vocabulary meaning, with no teacher’s intervention, whereas Group B, which received the same vocabulary lists, was taught the words, with no dictionary use allowed. Each time, the participants were tested on multiple choice vocabulary questions. They also completed a perception questionnaire, and 23 students were interviewed. The results of independent samples t-tests confirmed that teacher’s vocabulary instruction was significantly more effective than students’ dictionary use. However, the quantitative data of the perception questionnaire triangulated with the qualitative data of interview responses indicated that most of the students thought students’ dictionary use and teacher’s instruction of vocabulary yielded the same results.