The paper describes the case-history of the Beauregard dam (Italy), a concrete arch-gravity structure 132 m high built between 1951 and 1960 on the Dora di Valgrisenche River. The design reservoir volume was about 70 mil. m³. The geological and geotechnical investigations carried out since the dam construction and deepened in the last decade have underlined that a Deep-Seated Gravitational Slope Deformation (DSGSD) is located on the left slope. Since the first fillings of the reservoir, the interaction between the DSGSD and the dam was recognized to have relevant implications on the dam structural safety. For that reason, the Italian Dam Authorities in 1969 prescribed a limitation of the reservoir level with a corresponding reduction of the its volume to 6.8 million m³, about 1/10 of the initial design volume. The studies, which include a detailed analysis and thorough interpretation of the monitoring data over a time span of more than 50 years, have allowed to gain insights into the understanding of the DSGSD behavior and its interaction with the dam. To interpret the already experienced effects of the bank movements against the dam and to forecast the future possible trends, the numerical modeling activities have played a key role. The solution chosen to guarantee a long-term safety operation foresees the demolition of the upper part of the dam in order to drastically reduce the cracking pattern of the dam body caused by the compression of the vault for the DSGSD movement.