Performance of Borehole Thermal Energy Storage (BTES) systems depends on the temperature of the secondary fluid, circulating through the ground-loop heat exchangers. Borehole systems are therefore designed in order to ensure that inlet and outlet temperatures of the secondary fluid are within given operational limits during the whole life-time of the system. Monitoring the operation of the bore fields is crucial for the validation of existing models utilized for their design. Measured data provides valuable information for researchers and practitioners working in the field. A first data-set from an ongoing monitoring project is presented in this article. The monitoring system comprises temperature sensors and power meters placed at strategic locations within the bore field. A distributed temperature sensing rig that employs fiber optic cables as linear sensors is utilized to measure temperature every meter along the depth of nine monitored boreholes, yielding data regarding both temporal and spatial variation of the temperature in the ground. The heat exchanged with the ground is also measured via power meters in all nine monitored boreholes as well as at the manifold level. The BTES system is located at the Stockholm University Campus, Sweden, and consists of 130 boreholes, 230 meters deep. After more than a year of planning and installation work, some selected measurements recorded in the BTES during the first months of operation are reported in this article.