Feedback, or information given to learners regarding their performance, is found to facilitate second language (L2) learning. Research also suggests that the timing of feedback (whether it is provided immediately or after a delay) may affect learning. The purpose of the present study was to identify the optimal feedback timing for L2 vocabulary learning. This study differs from previous feedback timing studies in two important respects. First, unlike some previous studies, feedback timing was not confounded with lag to test (interval between the last encounter with a given item and the posttest). Second, in order to test the view that delayed feedback may be particularly effective when learners make few errors during learning, the present study manipulated the frequency of practice to influence learning phase performance. In this study, 98 Japanese college students studied 16 English-Japanese word pairs. Immediate feedback was given immediately after each response, whereas delayed feedback was withheld until all target items were practised. Learning was measured by posttests administered immediately, 1 week, and 4 weeks after the treatment. Results suggested that when lag to test is controlled, feedback timing may have little effect on L2 vocabulary learning regardless of the frequency of errors during learning.