BACKGROUND:: Family screening is a main step for the diagnosis in Wilson disease. This study was undertaken to evaluate the value of relative exchangeable copper for family screening. METHODS:: Data from family screening were collected from the French National Center of Reference for Wilson disease. Subjects who were first- or second-degree relatives of the index case underwent clinical examination and biological parameters. RESULTS:: Of 127 subjects examined, copper abnormalities or low ceruloplasminemia were detected in 21 subjects, corresponding to 5 patients with Wilson disease, 14 heterozygous ATP7B carriers and 2 subjects with no ATP7B mutations. Relative exchangeable copper determination significantly discriminates heterozygous ATP7B carriers and subjects with no ATP7B mutations from WD patients with a cutoff of 15%. CONCLUSIONS:: Exchangeable copper appears to be a promising tool for family screening in Wilson disease. © 2013 International Parkinson and Movement Disorder Society