The current study investigated the relationship between a measure of trait boredom (Boredom Proneness) and vigilance performance on a variation of Mackworth's original clock test. Performance, assessed as sensory efficiency, was negatively correlated with boredom proneness scores early in the vigil, but not during later trials. The results suggested that the trait of boredom proneness is predictive of performance on monotonous tasks within the first 10 minute block of trials. However, no difference in performance occurred on subsequent blocks, suggesting that as state boredom increases, differences between individuals diminish (e.g., a ceiling effect). The authors discuss the importance of examining boredom proneness as a multidimensional construct. Practical implications for these results are presented, particularly in terms of using "sensory efficiency" as a measure of performance in vigilance tasks.