Previous research has shown that Puerto Ricans are highly segregated from non-Hispanic whites and moderately segregated from blacks, with socioeconomic factors having no effect on these patterns. These findings are opposite those observed for other Hispanic groups and contradict the fundamental tenets of ecological theory. This paper explains these anomalous patterns and brings results for Puerto Ricans into conformity with prior theory and research on residential segregation. The Puerto Rican anomaly stems from their very low SES and their black ancestry. Law social status leads directly to high segregation, while a high percent of blacks among Puerto Ricans draws them strongly towards residence near non-Hispanic blacks. Since Anglos avoid living near blacks, Puerto Ricans become bystander victims of Anglos' racial prejudice, leading to their residential segregation in society.