Program comprehension is a cognitive psychological process. Accordingly, literature and intuition suggest that a developer’s intelligence and personality have an impact on their performance in comprehending source code. Some researchers have made this suggestion in the past when discussing threats to validity of their study results. However, the lack of studies investigating the relationship of intelligence and personality to performance in code comprehension makes scientifically sound reasoning about their influence difficult. We conduct the first large-scale empirical evaluation, a correlational study with undergraduates, to investigate the correlation of intelligence and personality with performance in code comprehension, that is, in this context, with correctness in answering comprehension questions on code snippets. We found that personality traits are unlikely to impact code comprehension performance, at least not when their influence is considered in isolation. Conscientiousness, in combination with other factors, however, explains some of the variance in code comprehension performance. For intelligence, significant small to moderate positive effects on code comprehension performance were found for three of four factors measured, i.e., fluid intelligence, visual perception, and cognitive speed. Crystallized intelligence has a positive but statistically insignificant effect on code comprehension performance. According to our results, several intelligence facets as well as the personality trait conscientiousness are potential confounders that should not be neglected in code comprehension studies of individual performance and should be controlled for via an appropriate study design. We call for the conduct of further studies on the relationship between intelligence and personality with code comprehension, in part because code comprehension involves more facets than we can measure in a single study and because our regression model explains only a small portion of the variance in code comprehension performance.