A routine audit revealed that in 25 per cent of patients with proximal femoral fracture, hospital stay was complicated by urinary tract infection (UTI). A prospective study was undertaken to investigate the relationship of UTI to fracture type, timing of surgery and the effect of perioperative antibiotics. Eighty-eight patients were investigated over a 4-month period with urine specimens obtained at time of operation and 48 h from operation. Of the patients, all female, 12.5 per cent had positive urine cultures at the time of operation. Of all patients, 42 per cent had positive urine cultures 48 h after operation. Females with intra-capsular fractures were more likely to have positive cultures both pre- and post-operatively (P < 0.005). Age (P < 0.05) and operative delay beyond 48 h (P < 0.05) were also found to predispose to infection. All patients except one who had urinary infection at the time of surgery had post-operative urine infection with the same organism. Present audit methods have significantly under estimated the presence of UTI in these patients. Fracture type and operative delay would appear to be the most significant determinants of a positive urine culture 48 h after operation. Prophylactic antibiotics appear to be ineffective in eradicating pre-existing or preventing early post-operative infection.