Three children aged 11 to 14 years with acute interstitial nephritis (AIN) are presented. In one patient AIN developed following antibiotic treatment with trimethoprim/sulfamethoxazole (TMP/SMX). In two patients no infection, drug, or toxin could be implicated. Severe polyuric renal failure without elevation of blood pressure was the predominant clinical feature. Uveitis occurred either simultaneously with the nephritic symptoms or several weeks after complete recovery of renal function. Renal functions were characteristically altered and led to suspicion of AIN even prior to renal biopsy. Renal plasma flow was relatively more reduced than glomerular filtration rate (GFR) with an accordingly increased filtration fraction. Quantitative evaluation of selective tubular functions revealed significant transport deficiencies for glucose, amino acids, inorganic phosphate and low molecular weight proteins. In two patients GFR increased rapidly following initiation of steroid treatment and tubular symptoms simultaneously disappeared. In one patient spontaneous remission occurred. We conclude that--in contrast to adults--the prognosis of AIN in childhood is favorable. Although general clinical features are rather nonspecific, symptoms of decreased tubular reabsorption ability provide a good indication of the diagnosis and may contribute to enhanced recognition of this disease.