The prognostic importance of hypertension at the onset of clinical lupus nephritis is not well established. We studied retrospectively 44 patients with lupus nephritis in order to ascertain the prevalence of hypertension at presentation and to investigate a possible association between hypertension and renal functional impairment. A correlation was also sought between hypertension and histological class of lupus nephritis. Hypertension was graded as mild (diastolic 95-99 mmHg), moderate (100-114) or severe (> 115). Impaired renal function (creatinine > 120 mumol/l) was graded as mild (120-200 mumol/l), moderate (200-350 mumol/l), or severe (> 350 mumol/l). Histological class and the presence of hypertensive renal vascular lesions was recorded. The prevalence of hypertension was 38%. There were 17 hypertensives and 27 normotensives. The incidence of renal impairment was greater in the hypertensives, 47% vs 18.5% (p = 0.04). Mean serum creatinine was also higher higher in this group (p = 0.02). The presence of hypertensive renal vascular lesions identified a high-risk subgroup who had a higher incidence of renal functional impairment and worse renal function than the hypertensive group as a whole. Even at an early stage, hypertension and hypertensive renal vascular lesions correlated well with renal functional impairment. Aggressive treatment of hypertension is therefore essential in early lupus nephritis in order to prevent further deterioration of renal function as the disease evolves.