Primary ciliary dyskinesia (PCD) is an autosomal recessive inherited disease characterized by abnormal ciliary motion and impaired mucociliary clearance. The prevalence of PCD is approximately 1 : 15 000 - 1 : 20 000 in live births. Cilia dysfunction is also implicated in a wider spectrum of diseases due to impaired organ genesis and body symmetry. Cilia are highly conserved in animals and show complex structures containing more than 250 proteins for their formation. Recent studies have begun to locate the PCD genes in the genome and characterize functional mutations. Specific diagnosis of the ciliary dysfunction requires physiological measurements as well as light- and electron microscopy. Abnormalities in ciliary motion and ultrastructural studies can be performed with nasal mucosal epithelium.