Hydroa vacciniforme is a troublesome and scarring photosensitivity disorder for which treatment is unsatisfactory. Dietary fish oil rich in omega-3 polyunsaturated fatty acids reportedly increases the resistance to ultraviolet-induced erythema and rash provocation in polymorphic light eruption. We report for the first time the response of hydroa vacciniforme to dietary fish oil. Three Caucasian boys with the condition were placed on MaxEPA, five capsules daily. Phototesting was performed at baseline and after 3 months supplementation. At baseline, low erythemal thresholds were seen to monochromated UVA at 350 and 370 nm in all three boys, while one also had a low threshold to 320 nm (UVA) and another showed a low threshold to 300 nm (UVB). Broad-band UVA provocation challenge produced typical skin lesions in all the subjects. Following fish oil, all the boys showed reduced erythemal sensitivity to UVA and one also showed reduced sensitivity to UVB. Provocation challenge revealed a reduced response in all three children. Clinically, these changes were accompanied by pronounced improvement in one child, mild improvement in the second child, but no improvement in the third. The third boy subsequently showed good clinical response to azathioprine.