To verify whether or not ciliary motility can be reliably assessed by light microscopy alone, we examined the nasal brushings of 53 patients with suspected ciliary dyskinesia and 10 healthy controls. The results of light microscopy were compared with cilia ultrastructure assessed with electron microscopy. Ciliary motility was significantly related with cilia ultrastructure. However, eight cases of lung disease due to bronchiectasis of unknown origin had immotile cilia on light microscopy, but normal ciliary ultrastructure on electron microscopy. Instances of normal and abnormal ultrastructure were detected in one case with motile cilia. There was an 83% agreement between electron microscopy and light microscopy. Sensitivity and specificity of light microscopy were 92% and 80%, respectively. In conclusion, light microscopy evaluation of ciliary motility does not appear to be a reliable screening test for ciliary dyskinesia because it does not quantify ciliary beat activity, which is a criterion for deranged ciliary motion. A complete evaluation of ciliary ultrastructure together with in vivo, if applicable, or in vitro function test (namely, the analysis of ciliary beat frequencies and/or waveform) is required for a definite diagnosis of ciliary dyskinesia.