The article reports on the findings of a study investigating the relationship between first language (L1) and second language (L2) fluency behavior. Drawing on data collected from Turkish learners of English, the study also addresses the question of whether proficiency level mediates the relationship, if any. The data were coded for a range of breakdown, repair, speed, and composite measures. Language proficiency was measured by means of two tests: Oxford Placement Test (OPT) and an Elicited Imitation Task (EIT). The results show that some breakdown and repair measures were positively correlated in L1 and L2, but no correlations were observed for articulation rate and speech rate. The relationships were not mediated by proficiency level. Regression analyses show that a number of models predicted L2 fluency. L1 fluency contributed significantly to models predicting pausing behavior; EIT scores predicted L2 speech rate; and L1 fluency and OPT scores predicted L2 repair and mid-clause pauses. The important implications of the findings for fluency research and second language pedagogy are discussed.