Hernia repair is one of the so-called clean operations. Many surgeons, however, use antibiotics, especially in the mesh repair era, without strong evidence to support this policy. We conducted a single-centre prospective randomised trial with a view to clarify this issue on a scientific basis. From January 2000 all patients undergoing elective inguinal hernia repair using a tension-free polypropylene mesh technique, provided they fulfilled predetermined criteria, were randomised to have a single dose of amoxicillin and clavoulanic acid or placebo in a double-blind manner. The main end point was to detect any difference in infectious complication rates - with specific interest to wound infection rates - between the two groups. Between January 2000 and June 2004, 386 patients entered the study (364 men and 22 women, median age 63 years, range 15-90 years) and were randomised to have antibiotic prophylaxis (group A, n = 193) or placebo (group B, n = 193). The two groups were comparable regarding demographic data. In total, 19 (5%) cases with infectious complications were detected. Fourteen of these were wound infections (3.7%). There were five cases of wound infection in group A and nine in group B (p = 0.4, Fisher's exact test). All wound infections were treated with antibiotics. The wound was opened in some cases. Mesh removal was not required in any of the cases. From the results of this study it does not appear that antibiotic prophylaxis offers any benefits in the elective mesh inguinal hernia repair.