Cognitive factors have been recognised as important in the interpreting process, but whether they could serve as valid components of interpreting aptitude still awaits further investigation. This study explores the predictive value of cognitive fluency in the simultaneous interpreting (SI) performance of trainee interpreters. Cognitive fluency measures of lexical access, lexical retrieval, linguistic attention control and working memory capacity were tested at the beginning of SI training. Simulated SI tasks were conducted at the start and the end of an intensive training period of one academic term. Results of the analyses suggest that (1) cognitive fluency measures could predict a large degree of variance in trainee interpreters' SI performance at the initial stage of SI training, but could only predict the SI performance when the cognitive load was comparatively high after training; and, (2) cognitive fluency constructs that were significantly related to SI performance differed before and after training. It is concluded that constructs of cognitive fluency might serve as predictors for interpreting performance, but the predictive value of cognitive fluency was influenced by cognitive load and interpreter training. Findings of the study provide empirical evidence for the inclusion of cognitive fluency tasks into interpreting aptitude tests.