RESUMEN
<p><b>OBJECTIVE</b>To observe the ultrastructural changes of sperm flagella in patients with severe idiopathic asthenospermia.</p><p><b>METHODS</b>Using the transmission electron microscope, we examined the ultrastructure of sperm flagella from 22 patients with severe idiopathic asthenospermia.</p><p><b>RESULTS</b>Ultrastructural anomalies were found in all the 22 patients, 6 with partial or complete absence of internal and external dynamic arms in dedicative of primary ciliary dyskinesia, 1 with hyperplasia, hypertrophy and disordered organization of the fibrous sheath usually referred to as dysplasia of the fibrous sheath, and the other 15 with non-specific flagellar anomalies.</p><p><b>CONCLUSION</b>Examination of the ultrastructure of sperm flagella in severe idiopathic asthenospermia patients can help to distinguish congenital from acquired flagellar structural anomalies and give valuable guidance in the treatment.</p>