The objective of this study was to assess isolated pyuria in an unselected systemic lupus erythematosus sample, and to determine factors potentially associated with this manifestation. We studied patients followed in our lupus clinic, defining isolated pyuria as more than 10 white blood cells per high power field in the absence of hematuria, proteinuria, casts, or bacteriuria. We assessed the effects of various demographic and clinical factors on the occurrence of isolated pyuria, using univariate logistic regression analyses. We also performed multivariate models which included sex, age, race/ethnicity, systemic lupus erythematosus duration, non-renal systemic lupus erythematosus disease activity, systemic lupus erythematosus damage, number of non-renal and renal American College of Rheumatology criteria ever present, pre-existing hypertension, and current drug exposures. Of 264 subjects, 66 were excluded (43 had bacteriuria or a contaminated urine culture and 23 had no concomitant urine culture); 27 of the remaining 198 (13.6%) had isolated pyuria. Sixteen of 27 patients with sterile pyuria had previous American College of Rheumatology criteria for renal involvement (hematuria, casts, and/or proteinuria) compared to 62/171 patients without sterile pyuria (unadjusted odds ratio = 2.55; 95% confidence interval = 1.11-5.85). Our univariate analyses also suggested a trend towards higher non-renal disease activity in patients with isolated pyuria. Independent associations were not evident in adjusted analyses. Isolated pyuria was observed in a significant number of our systemic lupus erythematosus sample. Although the differential diagnosis for isolated pyuria is broad, this manifestation may be correlated with lupus activity even in the absence of hematuria or proteinuria. Lupus (2010) 19, 793-796.