Sperm of patients with X-linked retinitis pigmentosa (RP) was studied to assess the state of the axoneme in this genetic subtype. Semen samples were collected from eight patients with X-linked RP and compared with a database of 31 controls. Semen was also collected from two patients with other retinal degenerations (choroideremia and fundus flavimaculatus) and patients with simplex RP. All controls and patients were studied under a masked protocol. There was a significant increase in the percentage of abnormal sperm tails at both the light and electron microscopic levels in patients with X-linked RP only. Thus, X-linked RP is associated with an alteration in sperm axoneme structure. Sperm cell analysis may serve as a useful model system for additional investigations into the pathogenesis of this disease.