To evaluate renal function after the use of a low-osmolality radiological contrast medium (CM), we prospectively analyzed 39 patients submitted to the following examinations: arteriography (n = 32), phlebography (n = 3), computed tomography (n = 3), angioplasty (n = 1), and retrograde pyelography (n = 1). The patients were divided into three groups: group 1, control, formed by renal donors (CT, n = 11 and 11 exams); group 2, hypertensive patients (HYPT, n = 15 and 16 exams); and group 3, patients with diseases of multiple etiologies (MIX, n = 13 patients and 13 exams). Additionally, the patients were divided according to their renal function into: group 4, with a moderate deficit of renal function, creatinine clearance (CrCl) 25 to 60 mL/min (n = 15 patients and 15 exams); and group 5, with a mild deficit of renal function, CrCl > or = 60 mL/min (n = 14 patients and 14 exams). The CM utilized was ioxaglic acid (Hexabrix) the incidence of acute renal failure (ARF) among the patients studied was 12.5% (5/40), and CrCl was the best parameter to monitor the alterations in renal function, which occurred in 35% of the patients, although the changes were mild, reversible, and did not need any therapeutic interventions. The triggering of ARF in these patients may have been due to multiple factors presented at time of CM examination. Thus, it is not possible to identify a single risk factor. However, it is probable that previous important impairment of renal function was the most expressive risk factor.