Over the past 2 decades, research has demonstrated that learner collaboration facilitates second language (L2) acquisition (Lapkin, Swain, & Smith, 2002; McDonough, 2004; Storch, 1998, 2004; Swain & Lapkin, 1998). Adopting a sociocultural perspective (e.g., Swain & Lapkin, 1998), the current study compared the effectiveness of collaborative and individual tasks on the acquisition of L2 vocabulary by Korean as a second language (KSL) learners (N = 32). The learners completed a pretest, a dictogloss task, and two posttests over a 3-week period. Half the learners carried out the dictogloss in pairs, but the other half worked individually while thinking aloud. The collaborative dialogue and think-aloud protocols were transcribed, and language-related episodes (LREs) were identified. The results indicated that although the learners who participated in the collaborative task had a similar number of LREs as the learners who worked individually, they performed significantly better on the vocabulary tests. The pedagogical implications for the use of collaborative tasks to promote the acquisition of L2 vocabulary are discussed.