BHD syndrome is a rare autosomal dominant inherited disease in which fibrofolliculomas, trichodiscomas, renal tumours and pneumothorax caused by lung cysts can occur. The pathophysiology is largely unknown. We show that BHD syndrome is a ciliopathy in which the causal protein, folliculin, is located in the primary cilium. In folliculin knockdown cells, less cilia are observed. Further research will give more insight into the pathophysiology of BHD syndrome.