One hundred serial sections from each of 128 cases with immunoglobulin A (IgA) nephropathy were examined by light microscopy to clarify the relationship between segmental glomerular necrosis (SGN) and progression of glomerular injury. The cases were divided into five groups according to the percentage of glomeruli with cellular/fibrocellular (C/F) crescents, fibrous adhesion and/or sclerosis: grade I, 0%; grade II, < 20%; grade III, 20-50%; grade IV, 50-80%; and grade V, 80% or more. The serial sections revealed unequivocally focal occurrence of SGN in 39 cases (30%). Segmental glomerular necrosis was never found in the cases of grade I (0%, 0/28), while it appeared in those of grade II (33%, 12/36), grade III (46%, 13/28), grade IV (48%, 13/27) and grade V (11%, 1/9). The incidence of the cases with C/F crescents showed a similar tendency among the groups. In addition, focal C/F crescents were more frequent in cases with SGN (82%) than in those without SGN (24%). In particular, cellular crescents in 26 cases were formed in close proximity to SGN. These results suggested that SGN in IgA nephropathy was a more common finding than formerly evaluated and that it potentially participated in the progression of glomerular injuries closely associated with crescent formation. Unequivocally, focal occurrence of SGN corresponded well with the slowly progressive course of the glomerular disease.