Given the heritability of human left-handedness and its purported associations with fitness-lowering traits, the persistence of the minority of left-handedness in human populations is an evolutionary puzzle. The fighting hypothesis proposes that these negative fitness costs are offset by fitness gains for left-handers when involved in fights with right-handers, as being a minority would generate a surprise effect increasing the chance of winning. The finding that left-handers are overrepresented in many combat sports is interpreted as evidence for this hypothesis. However, few studies have examined sports that show good similarity with realistic fights and analysed winning chances in relation to handedness of both fighters. We examined both, in a sample of the Ultimate Fighting Championship (UFC), a fierce fighting sport hardly constrained by rules. Left-handers were strongly overrepresented as compared to the general male population but no advantage for left-handers when facing right-handers was found, providing only partial evidence for the fighting hypothesis. © 2013 The Association for the Study of Animal Behaviour.