To determine the impact of a co-payment on the cost-effectiveness of systematic screening for diabetic retinopathy in Hong Kong (HK). An analysis was conducted from provider and societal perspectives. A Markov cohort model was used to determine the cost-effectiveness of screening with a co-payment of HK$60 (US$7.7) compared with free screening, with and without an assumption that the inverse care law (ICL) would operate in the presence of a fee as seen in our previous data.