A series of 76 pyonephrotic kidneys in 73 patients were drained by percutaneous nephrostomy (PN) tube and examined to evaluate the contribution of this technique to the treatment of pyonephrosis. In 71 patients, clinical symptoms disappeared 24-48 h after the procedure. Two patients died from sepsis subsequent to anuria and underlying malignancy. Once the acute phase had remitted, interventional procedures were carried out in 39 cases, and constituted the definitive therapy in 36. In 32 cases, elective surgery was the definitive therapy, including the 3 cases not resolved after interventional procedures. Three patients in whom the obstruction cleared spontaneously following PN needed no additional treatment. Major complications included 6 cases of sepsis, all of which resolved satisfactorily with proper medical therapy.