The prevalence of primary ciliary dyskinesia syndrome (PCDS) in Western countries is of 1/40,000 but is 13% in patients with bronchiectasis. The aim of this study was to determine the prevalence of PCDS in patients with bronchiectasis and sinusitis, including whether or not these patients present specific clinical signs. Eighteen patients with these two conditions from an area with 750,000 inhabitants in Valencia (Spain), were studied for 2 years. Radiologic and clinical information was recorded and mucociliary motility was measured with albumin marked with radioactive technetium. The structure of the nasal mucosa cilia was also studied. In 14 patients (77%) mucociliary motility was suppressed and in 13 ultrastructural changes typical of PCDS were observed. Only male infertility and situs inversus were more frequent in patients with PCDS; other clinical signs were equally severe and frequent in patients with PCDS and in those in whom no cause for bronchiectasis and sinusitis could be found. We conclude that 1) the prevalence of PCDS in patients with bronchiectasis and sinusitis is 77%; 2) in these patients a test of mucociliary motility is sufficient for diagnosis (structural study not being required); 3) the prevalence of PCDS in our population seems to be greater than that described; and 4) clinical signs are similar in patients with PCDS and in those with bronchiectasis of unknown genesis.