A 38-year-old male with a history of 11 years' involuntary infertility was investigated at a subfertility clinic. Seminal analysis showed a sperm density of 40 to 50 × 106 spermatozoa/ml and 1 to 2% motility. He had a normal male complement of 46 chromosomes and meiotic analysis showed 23 normal bivalents. The testes appeared normal histologically, but in the biopsy specimen abnormal spermatozoa were detected in the seminiferous tubules by electron microscopy. Electron microscope examination showed that 97% of ejaculated spermatozoa were structurally abnormal, with elongation of the mid-piece, absence of an outer sheath on the main-piece and extra axial fibres.