Interactions between PAOs and GAOs in EBRP systems have been reported as one of the major causes of EBPR failure. This study investigated the abundance of the PAO species Candidatus accumulibacter phosphatis and the GAO species Candidatus competibacter phosphatis in a fullscale well performing EBPR system. General changes in the microbial population of the system were also assessed. The molecular tools Fluorescence in situ Hybridization and Terminal- Restriction Fragment Polymorphism were applied. The results confirmed that the system achieved excellent P removal performance and had a stable microbial population during the study period. It was also observed that the targeted GAO species was more abundant in the microbial population than the targeted PAO species. The results contradict the reports that GAO presence is typically related to EBPR failure, which points to the need for further investigation of the interactions between PAOs and GAOs in full scale EBPR systems.