Proteinuria is a relatively frequent complication in children after renal transplantation (40-80 %). It is usually mild and non-nephrotic in nature and predominantly tubular in origin. The major causes of post-transplant proteinuria are recurrence of primary glomerulonephritis [mostly focal segmental glomerulosclerosis (FSGS)], rejection (acute and chronic), mTOR inhibitors or hypertension. Proteinuria is a risk factor for graft loss and patient death in adults, and even a mild proteinuria (0.1-0.2 g/day) is associated with impaired graft and patient survival. In children, proteinuria seems to be associated with graft but not patient survival. Proteinuria (protein/creatinine ratio) should be assessed regularly in all children. In children with prior chronic kidney disease due to idiopathic FSGS, proteinuria should be assessed daily during the first month after transplantation to enable early diagnosis of recurrence. The cause of proteinuria should be identified, and graft biopsy should be considered in children with unexplained proteinuria, especially with new onset proteinuria or deterioration of previously mild proteinuria. Treatment must be primarily targeted at the cause of proteinuria, and in normotensive children symptomatic antiproteinuric therapy with angiotensin-converting enzyme inhibitors/angiotensin II receptor antagonists should also be initiated. Other antihypertensive drugs should be used to achieve target blood pressure of <75th percentile. Target proteinuria should be <20 mg/mmol creatinine.