In this study, we have evaluated 50 children (30 girls and 20 boys; mean age, 10.1 years) with a variety of renal diseases in whom renal biopsy specimens showed crescents in greater than or equal to 50% of glomeruli. Initial clinical features included edema in 61%; hypertension in 51%; gross hematuria in 73%; 3 to 4+ proteinuria in 78%; and severely decreased GFR (less than 30 ml/min/1.73 m2) in 66%. When the total number of patients was divided into those with 50 to 79% crescents (N = 18) and those with 80 to 100% crescents (N = 32), no significant difference in outcome could be demonstrated, with endstage renal disease (ESRD) being seen in 44 and 52% of the two groups, respectively. Pathologic features associated with a poor prognosis included predominance of large crescents (P = 0.004) or fibrous crescents (P = 0.03); increased frequency of gaps in Bowman's capsule (P = 0.004); global glomerular sclerosis (P = 0.05); glomerular IgM (P = 0.003); interstitial fibrosis (P = 0.03); and tubular atrophy (P = 0.04). At followup, GFR was normal in all patients with poststreptococcal GN, but low in 60% of patients with other conditions. The study permits the following conclusions: (1) Approximately 50% of children with crescents in 50% or more glomeruli progress to ESRD; (2) a poor prognosis is associated with (a) a high percentage of large crescents, (b) increased frequency of gaps in Bowman's capsule, and (c) evidence of chronic histologic changes, but not with the percentage of crescents per se; and (3) the underlying type of glomerulonephritis is considered a helpful prognostic indicator.(ABSTRACT TRUNCATED AT 250 WORDS)