What is the proper way to manage complicated primary mega-ureter in infants under the age of one. This has already been discussed in the literature but the controversy remains. Evaluate the long-term results of the management of mega-ureter based support under the age of one. Single-center retrospective study from 1990 to 2010. All children under one year found were evaluated including clinical examination, ultrasound, scintigraphy and cystography. They were divided into two groups: group 1: children operated on before the age of one year, group 2 non-operated or operated children after the age of one year. We analyzed the long-term evolution of these children on the following criteria: reflux, pyelonephritis, changes in dilation, renal function, need for surgical revision or secondary surgery, and impact on bladder function. In total, 54 patients were included in group 1 and 56 patients in group 2. In a median follow-up of 12years. A total of 101boys and 9girls (sex-ratio 11.22). There were 57 left MUP (52%), 22 right (20%) and 31 bilateral (28%). A total of 71% of antenatal diagnosis. No difference on the emergence of complications: 25 (group 1) versus 31 (group 2) OR=0.69; 95% (0.307; 1.574); P=0.44. No difference between secondary surgery and revision surgery: group 1=12, group 2=22, OR=0.45; 95% CI (0.17, 1.09); P=0.06. No difference for daytime incontinence: OR=1.04; 95% CI (0.14; 7.64); P=0.67. Seventy-six children (69%) were finally made, 12 children operated twice (10.9%) and 34 children (31%) never made. The main challenge of the MUP of management is the preservation of renal function. Sixty-nine percent of our children received surgery due to impaired renal function lower than 30% of urethral dilatation greater than 10mm associated with reflux or recurrent pyelonephritis. Clinical monitoring, regular ultrasound and isotopic testing are necessary and should be extended to adulthood. 5.