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Background: A light-coloured iris is considered a risk factor for skin cancer in general. However, iris colour cannot be considered a plausible risk factor for skin cancer in East Asian populations because of the relative homogeneity of iris colours. Furthermore, subjective classifications of iris colour cannot distinguish between different East Asian individuals as to their likelihood of developing cancer., Aim: To measure human iris colours quantitatively and to assess the significances of iris colours with respect to skin cancer in Korean patients., Methods: Reference Commission Internationale d'Eclairage (CIE) L*a*b* coordinates on a ColorCheck chart were recorded using a reflectance spectrophotometer and compared with computed CIE L*a*b* coordinates from digital images to determine equations to calibrate CIE L*a*b* values. We then took iris images and measured iris colours and the colours of sun-exposed and sun-protected skin in 42 Korean patients with various cutaneous malignancies and nonmalignant dermatological diseases. Results were statistically analysed with regard to iris and skin colours in CIE L*a*b* coordinates., Results: Patients with skin cancer had significantly lighter irises or higher L* values than dermatological patients without a malignancy (P = 0.02). Colour differences (ΔE*ab) between sun-exposed skin and sun-protected skin were greater in men (P < 0.01) and in patients with skin cancer (P < 0.01), and the lightness (L*) values of sun-exposed skins decreased with age (r = -0.32, P < 0.05)., Conclusions: Iris colour appears to be a possible skin cancer risk factor in East Asian populations. The larger colour differences seen between sun-protected and sun-exposed skin in men and in patients with skin cancer may have been due to chronic or excessive sun exposure., (© 2009 The Author(s). Journal compilation © 2009 British Association of Dermatologists.)