Objective: The study aimed to identify the variation of biological parameters recorded at the patients with obstructive renal failure treated with percutaneous nephrostomy. Material and method: The retrospective study investigated the data of 244 patients admitted in our department and treated with percutaneous nephrostomy for obstructive renal failure during January 2005 – December 2007. Demographical data, investigation, operation notes, indication, biological parameters trends (creatinine, haematocrit, haemoglobin, kaliemia, alkaline reserve), complications and hospital stay were recorded. The biological parameter trends (creatinine, haematocrit, haemoglobin, kaliemia, alkaline reserve) was analysed. The median preoperative and postoperative values of those parameters was compared. Statistical analysis was performed.Results: The median preoperative/discharge values of creatinine were 8.29mg%(1.6-26.3 mg%) comparing to 3.63mg% (0.64-13 mg%). A return to normal renal function at the discharge time was noted in 23 patients (9.7%). Hyperpotasemia (K>5.1mEq/l) on admission was found in 134 patients (54.9%). The median preoperative/discharge values of potassium were 5.71mEq/l comparing to 4.8 mEq/l.The median hospitalization time was 8.7 days with a median ICU stay of 3.3 days. The recorded mortality was 3.2% (8 patients) with an average time of 5.8 days between the operatory time and exitus time. Conclusions: The most frequent causes of obstructive renal failure necessiting percutaneous nephrostomy are malignancies. After renal percutaneous drainage the renal function improvement is fast and significant. In the postoperative period the onset of severe hypokalemia call for aggressive treatment in the same time with volume repletion.