It is established that reading and reading-related processes are heritable; genes thus play an important role in the foundation of individual differences in reading. In this article, we focus on one facet of reading–comprehension. Comprehension is a higher order cognitive skill that requires many other cognitive processes for it to unfold completely and successfully. One such process is executive functioning, which has been associated with genetic variation in the catechol-O-methyltransferase (COMT) gene. Genotypes and haplotypes of four single nucleotide polymorphisms in COMT were investigated in 179 incarcerated adolescent delinquents. Four hierarchical logistic regression models predicting the presence/absence of comprehension difficulties were fitted to the data; genetic variation in COMT and the presence/absence of maternal rejection were investigated as main effects and as effects acting interactively. Three out of four interaction terms were found to be important predictors of individual differences in comprehension. These findings were supported by the results of the haplotype analyses, in which the four investigated polymorphisms were considered simultaneously.