Questions about how jurors understand and apply scientific evidence were addressed in a mock jury study in which 480 jury pool members watched a videotaped mock trial that included expert testimony about mitochondrial DNA (mtDNA) evidence purportedly linking a defendant to a crime. Collectively, jurors showed moderately good comprehension of the mtDNA evidence, although some made definitional and inferential errors. Comprehension was better among jurors with higher educational attainment and more mathematics and science courses. Lower comprehension was associated with jurors' reservations about science and concerns about the contamination of mtDNA evidence. The results suggest that most jurors are capable of comprehending and employing scientific evidence presented during trial, although errors and doubts about the evidence should be anticipated.