Dense intramembranous deposit disease (DIDD) almost universally recurs in renal allografts. However, the 29 previously reported cases suggest that recurrent DIDD rarely results in graft failure. We studied the clinical course and renal histology of the 6 patients with DIDD who have received renal allografts here since 1967. All patients had characteristic findings of DIDD in their native kidneys by light, immunofluorescence and electron microscopy. Seven grafts in 4 patients failed and histological evaluation showed that 5 of these allografts in 4 patients were lost due to recurrent disease. They all demonstrated marked mesangial proliferation with crescents but minimal acute interstitial or vascular changes of rejection. Patients with graft failure due to recurrent disease were male and developed recurrent nephrotic syndrome. The 2 patients with rapidly progressive glomerulonephritis (RPGN) in their native kidneys lost the transplanted kidney due to recurrent disease within 1 year. This study suggests that recurrence of DIDD in renal allografts is a more serious problem than previously appreciated, especially in patients with RPGN.