We performed a retrospective study on 47 children over 1 year of age with severe acute renal failure (ARF) treated with hemodialysis (HD) at our Center from 1978 to 1986 in order to evaluate the diagnostic and prognostic value of growth indexes at hospital admission as a criterion to distinguish cases of ARF without previous chronic renal failure (CRF) from cases in which CRF was not previously diagnosed. The age of the patients ranged from 17 months to 13 years. The cause of ARF was identified in 41 children; 5 of them remained on HD for different reasons (hemolytic uremic syndrome with arteriolar involvement in 3 cases; renal vein thrombosis in 1; endoextracapillary glomerulonephritis in 1). No apparent cause of ARF was found in the other 6 children who remained on chronic HD. A careful history showed that these 6 children had had uremic symptoms for many years. When height was expressed as height standard deviation score (HSDS), the 6 children with ARF of unknown etiology showed significantly lower HSDS values compared with the other 41 children in whom a cause of ARF was diagnosed (p less than 0.001). In conclusion, growth failure in children requiring HD for ARF of unknown etiology is an important criterion that suggests a previously undiagnosed CRF and thus consequently a negative long-term prognosis.