Background A varicocele is an abnormal tortuosity and dilation of the testicular veins within the spermatic cord. The incidence of varicocele in AS, which affects predominantly young male individuals, is unknown.

Objectives We proposed to assess the incidence of varicocele in AS evaluated by physical examination and colour doppler ultrasonography (CDU). Sperm parameters of these patients were also investigated and compared with controls.

Methods Thirteen untreated male patients (ages 18–40) with AS and age matched healthy 12 male subjects (ages 18–39) included in the study. Testicular veins in both groups were studied with CDU and semen samples were analysed.

Results Eight of the patients evaluated with physical examination had varicoceles (all grade II, 5 left side, 3 bilateral). Only two subjects in control group had grade II varicocele on the left side and both were asymptomatic. Colour doppler evaluation of the testicular vessels in patients with AS revealed grade II varicocele (6 left side, 3 bilateral) in 9 of the patients (69,2%) examined. Semen parameters were within normal limits in 7 patients, and there were altered sperm count and quality in 6 patients.

Conclusion The high incidence of varicocele in patients with AS may be explained by chronic inflammatory low-back pain that brings about reduced extensor muscle strength that causes compensatory increase in intra-abdominal pressure. This may cause a mechanical overload to the testicular vessels. Secondly, vasodilator effect of nitric oxide that was activated by inflammatory process.