Early and accurate detection of kidney involvement in systemic lupus erythematosus (SLE) improves outcomes. Renal biopsy is required for definitive diagnosis of lupus nephritis (LN). In the absence of acute renal failure (ARF), moderate levels of proteinuria (> 1000 mg/24 h) have been recommended by some to justify biopsy. We investigated whether patients with lower levels of proteinuria without ARF have significant renal disease and should be routinely biopsied. We retrospectively evaluated 21 SLE patients with 24-h urine protein < 1000 mg who underwent kidney biopsies. Indications for biopsy included new-onset proteinuria, increasing proteinuria, or hematuria (> 5 red blood cells per high power field). No patient had ARF. Sixteen of 21 (77%) biopsies were diagnostic of LN: 3 class II, 10 class III (5 superimposed class V), 2 class IV (one superimposed class V), and one with class V. One patient had thrombotic microangiopathy. The remaining 4 (23%) patients had non-lupus renal disease. Thirteen patients with class III or greater LN required alterations in therapeutic regimen because of biopsy findings. Of 7 patients without hematuria at the time of biopsy, 4 (57%) had class III, IV, or V LN. One patient without hematuria and < 500 mg/24 h proteinuria had class III LN. We found significant renal involvement (Class III, IV, or V LN) in SLE patients with < 1000 mg proteinuria with or without hematuria. Our findings suggest that biopsy be strongly considered in this patient population.