Cloning of the gene defective in the X-linked neurodegenerative disorder Menkes disease led to a cascade of new findings. Besides giving a better understanding of the intracellular copper homeostasis, these findings had important consequences from a clinical point of view. Today the underlying genetic defect has been described in several patients affected by one of the three hereditary disorders of copper metabolism: Menkes disease, occipital horn syndrome and wilson disease. In this review we discuss mainly Menkes disease and the impact of the recent findings on the diagnosis of this disorder.