Screening programmes for haemochromatosis that include follow-up identification of relatives are claimed to be cost effective. We assessed uptake of screening by first-degree relatives of two groups of index cases: people homozygous for the C282Y mutation ascertained by genetic screening of blood donors; and patients presenting clinically with haemochro matosis. Only 40 (24%) of 165 relatives of blood donors had been tested. By contrast, testing uptake in 121 relatives of patients diagnosed clinically was more than double that (53%), despite unstructured provision of genetic information. A substantial number of untested relatives had undiagnosed iron overload. Overall efficacy of population screening for haemochromatosis is undermined by these observations.