This paper discusses the monitoring of Palazzo Lombardia, one of the tallest high-rise buildings in Italy. First, the layout of the monitoring system is addressed for a general description of the sensors used. The paper provides details about how data coming from transducers are used. Special focus is put on the use of signals acquired by means of accelerometers, which are employed for the estimation of modal parameters through operational modal analysis. The procedure used for choosing the modal analysis algorithm and fixing the values of its main parameters is discussed in detail. The modal identification results on the first eight months of monitoring are discussed in the second part of the manuscript, together with a statistical analysis. This allows for a first model of the relationships between eigenfrequencies and environmental variables aiming at a general structural health monitoring procedure based on the evolution of the building’s modal parameters.