Our objective was to use factor analysis as a data reduction tool to organize a large number of placental pathologic features into useful aggregates. We examined 1146 placentas of live-born infants with a birth weight of 500-1500 g. We then conducted analyses of pairs of characteristics and multiple characteristics to identify "associated groups" and "factors," respectively. We found an associated group and factor that had placental features associated with acute inflammation and another associated group and factor that had features associated with vasculopathy. Acute umbilical vasculitis had the strongest correlation with other features of the acute inflammation associated group and factor. Gross evidence of acute inflammation (opacification and green appearance of membrane) was eliminated in the reduction from associated group to factor. Infarcts and syncytial knots were strongly dissociated with features of acute inflammation. The multiple pathologic features of the very low birthweight placenta can be aggregated into two associated groups or two factors. Lack of membrane opacification cannot be used as a criterion for declining microscopic examination. The absence of infarcts and syncytial knots should prompt a search for features of acute inflammation. If a placenta has two or more findings from the acute inflammation factor or the vasculopathy factor, it is unlikely to demonstrate features from the other factor.