BACKGROUND Bacteriuria > or = 10(5) CFU/ml is evidence of urinary tract infection in the absence of associated signs or symptoms. The presence of pyuria with asymptomatic bacteriuria established the response of elderly women against microorganisms capable of causing invasiveness or tissue injury of the urinary tract. METHODS The association between bacteriuria and pyuria was determined in 178 elderly, ambulatory women without symptoms of urinary tract infection in seven nursing homes. Urine culture results were subsequently analyzed in conjunction with absolute leukocyte count in urine. In this cross-sectional study, asymptomatic bacteriuria in elderly women was classified with and without pyuria. RESULTS The prevalence of asymptomatic bacteriuria was found in 44 (24.7%) elderly women. The presence of pyuria had a sensitivity of 63.6% for bacteriuria and a specificity of 91%. The positive predictive value for the presence of pyuria predicting those with bacteriuria was 70%, and the negative predictive value for the absence of pyuria predicting those without bacteriuria was 88.4%. Escherichia coli was the most common organism isolated in 81.8% of the women. CONCLUSIONS Bacteriuria > or 10(5) CFU/ml associated with pyuria was detected in 77% of elderly women with asymptomatic urinary tract infections. Bacteriuria of < 10(5) CFU/ml with pyuria proves less sensitive as an indicator of urinary tract infection. Elderly women with pyuria but without bacteriuria should be studied for other causes of urinary tract inflammation.