Between 1962 and 1970, 36 children with acute biopsy-proven poststreptococcal glomerulonephritis (PSGN) entered a prospective long-term follow-up study. The initial biopsies were scored into four histological grades using criteria based on endocapillary proliferation, leucocyte infiltration, epithelial "hump" and crescent formation; 5 patients had grade-1 (least severe), 14 grade-2, 15 grade-3 and 2 grade-4 biopsies. Two children died from rapidly progressive glomerulonephritis; both had grade-4 biopsies. Early repeat biopsy in 12 patients showed improvement in all but one patient who progressed from grade 2 to type 2 mesangiocapillary glomerulonephritis (MCGN). The initial biopsy grade correlated significantly with heavy proteinuria (chi2 = 9.73, P less than 0.01) but not with hypertension, haematuria or renal functional impairment. Follow-up observations were made after mean periods of 9.5 years (range 5.4-12.4 years; 32 subjects) and 19.0 years (range 14.6-22 years; 30 subjects). None of the survivors had an abnormal plasma creatinine. Only one patient (grade-3 biopsy), a female with a subsequent history of recurrent pyelonephritis, was hypertensive. Isolated microscopic haematuria persisted in 1 grade-2 and 2 grade-3 subjects. One grade-2 subject had proteinuria secondary to MCGN and one grade-3 subject had mild proteinuria and borderline hypertension. Although 20% of subjects had urinary abnormalities, we conclude that the long-term outcome of PSGN in children is excellent.