Silybum marianum (milk thistle) has been used for centuries as a herbal medicine for the treatment of liver diseases. Its purified active fraction, silymarin, is applied in treatment of liver diseases of toxic and viral origin in the modern therapy. The plant and its products are applied in the treatment of patients suffering from Wilson's disease as well with the aim of protecting liver from the consequences of copper accumulation. Based on the available data we hypothesized that products prepared from milk thistle may include copper in significant amount. Preparations with high copper content may be real danger for patients. Our aim was to examine this hypothesis and measure the copper content of different products by ICP-MS. The copper content of the daily doses of the examined preparations ranged between 0.01 – 114.18 µg. For patients suffering in Wilson's disease copper-free diet is recommended and milk thistle preparations containing a high concentration of copper significantly increase the copper load and therefore can be regarded as undesirable during the treatment. The copper contents of samples containing silymarin, the purified flavonolignan complex of milk thistle fruits, were rather low (0.01 – 3.51 µg in the daily dose). However, products based on Silybum extracts other than of silymarin or ground plant material contained copper at concentrations which were magnitudes higher than silymarin (36.04 and 12.04 – 96.50 µg in the daily dose, respectively). These results emphasize that the preparations of the copper-concentrating milk thistle may greatly vary in copper content. The method of extraction has major impact on the copper content therefore in the treatment of Wilson's disease, products containing silymarin should be preferred. Acknowledgements: This research was supported by the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TAMOP 4.2.4. A/2 – 11 – 1-2012 – 0001 'National Excellence Program'.