The density of diffuse, primitive, classic and compact Β/A4 deposits was estimated in the cortex and hippocampus in Alzheimer's disease (AD) cases with and without pronounced congophilic angiopathy (CA). The total density of Β/A4 deposits in a given brain region was similar in cases with and without CA. Significantly fewer diffuse deposits and more primitive/classic deposits were found in the cases with CA. The densities of the primitive, classic and compact deposits were positively correlated in the cases without CA. However, no correlations were observed between the density of the mature subtypes and the diffuse deposits in these cases. In the cases with CA, the density of the primitive deposits was positively correlated with the diffuse but not with the classic deposits. The data suggest that the mature Β/A4 deposits are derived from the diffuse deposits and that the presence of pronounced CA enhances their formation.