This study examines the effects of an online workbook and a paper workbook on L2 vocabulary acquisition. Participants consisted of 549 L2 learners of Spanish enrolled in a large language program at an American state university. The participants received 4 hours of classroom instruction per week and worked with an online or a paper workbook once a week during two semesters. They also completed a screening test and four vocabulary tests: two during the first semester and two during the second semester. The results showed no significant differences between the online and the paper workbook groups after one semester of instructional treatment. However, the online workbook group proved better than the paper workbook group in the second semester. These findings confirm results of previous studies on the beneficial role of CALL on L2 vocabulary acquisition, and they point to the pedagogical advantages of online workbooks for large language programs as long as enough length of exposure to the online environment is allotted. (Contains 2 tables and 7 figures.)