Studies in adults with chronic kidney diseases demonstrate that the orally available angiotensin II antagonist irbesartan reduces arterial pressure and pathological proteinuria, mostly with an excellent tolerability profile. Little information is available on irbesartan in childhood. A total of 44 pediatric outpatients with chronic kidney disease (27 male and 17, aged 3.7 to 18 years, median 10 years) were given irbesartan once a day during 18 weeks for arterial hypertension ( N = 23), proteinuria ( N = 8), or both ( N = 13). In patients with hypertension, the use of irbesartan 4.1 (3.1–5.3) mg/kg body weight daily (median and interquartile range) was associated with a decrease ( P < .005) in arterial pressure by 17 (13–22)/10 (7–12) mm Hg. In patients with overt proteinuria the urinary protein excretion decreased ( P < .01) during treatment with irbesartan (2.9 2.0–4.8 mg/kg body weight) by 52 (0–75) mg/m 2 × h), whereas plasma albumin increased ( P < .05) by 4 (1–5) g/L. The frequency of abdominal pain, constipation, cough, diarrhea, dizziness, edema, fatigue, headache, insomnia, myalgia, orthostasis, and rash was similar before and with irbesartan. Plasma sodium slightly decreased, whereas plasma potassium increased, with irbesartan ( P < .01). In pediatric patients with chronic kidney diseases, irbesartan given once a day for 18 weeks significantly reduces arterial pressure and proteinuria, with an excellent tolerability and side effect profile.