The Golden Horn Estuary, Istanbul, Turkey, had been exposed to untreated industrial discharges and municipal wastewater for over fifty years; however, during the last fifteen years pollution has been reduced due to an extensive rehabilitation campaign. Since sediment is the main accumulation matrix of marine ecosystems, surface sediment samples were collected from the estuary and analyzed for concentrations of some elements and radioactivity. The elements of predominant anthropogenic origin such as As, Cu, Pb, Sb, Sn and Zn and 137Cs were observed in the mid-estuary. Also, elevated geoaccumulation indices for Ag, Cd, Cu and Sb showed that pollution was still occurring in the estuary despite the rehabilitation. There is a huge residential area near the estuary; therefore, people living in this area are affected due to the pollution of the estuary. Thus, the obtained data of the elements and radionuclides are very important for the ecosystem of the Golden Horn.