Numerous authors have long felt that there is an association between malignancy and membranous glomerulonephritis. Most physicians have not noticed this association since the number of patients that they clinically observe is so low that such a relationship might not be obvious. The present study was undertaken to establish whether the relationship is real and to determine exactly how prevalent. Our results indicate the relationship definitely does exist, confirming studies that have shown a relationship based on positive staining for cancer antigens in kidney biopsy specimens. In addition, the study indicates that malignancy will become detectable within a relatively short period after the diagnosis of membranous glomerulonephritis, and that the malignancy rate is five times greater than the incidence in a baseline population. This risk is also highest in the elderly.