The purpose of this study is to explore L1 use in L2 writing from the perspective of Vygotskian Sociocultural Theory (SCT). We examine whether generating ideas in L1,compared to generating ideas in L2, results in inferior L2 writing. The participants were 42 Korean EFL students. As part of the course requirements, the students were required to hand in 400-word essays on a given topic. Once the writing was completed,they were asked to write down about what language(s) they used to prepare for the assignment and why they used this language or these languages. The data analysis used here stems from two ways in which the data were coded, use of language(s) during idea generation and a global-level essay analysis. This study has shown that more than half of students use their L1 while writing in L2 to some extent. Regarding the effect of L1use on L2 text quality, L1 use does not appear to be negatively related to L2 text quality. This does not confirm the results of earlier research, which suggested that L1use has a detrimental effect on L2 text quality. We argue that the L1 is an already internalized and very effective meditational means that learners will resort to,principally for discovering and shaping meaning and as support in moments of cognitive difficulty.