Background: Assuming that flavonoids have anti-oxidative properties and may protect against abnormal skin reactions in erythropoietic protoporphyria (EPP), we investigated whether systemic treatment with hydroxyethylrutosides (2.7 g/day) could decrease skin sensitivity to blue light in a 37-year-old female patient who suffered from EPP. Design and Results: Before treatment, skin exposure during 5 min to a xenon high-pressure gas discharge lamp with filter was sufficient to produce intense erythema, irritation and later swelling. After 1, 2 and 3 months of treatment, the exposure times, necessary to produce similar effects, gradually increased. This improvement coincided with an increased tolerability to sunlight. No adverse effects were observed. Conclusion: These results encourage the set-up of a more systematic, placebo-controlled study of the protective effects of hydroxyethylrutosides in EPP.