This paper presents a study of the stability of a steep rock slope, hanging over an active mine site, and a busy road. The overall assessment of the rock mass geometry and mechanical characteristics is carried out by means of both field survey and laboratory tests. The stability of the slope and its possible evolution are evaluated using the Itasca distinct element code UDEC 4.0. The results of the analyses show that heavy and prolonged rainfall is an important triggering factor for major rockfall activity. The slope instability currently concerns only blocks of relatively small size. The possibility of instability of larger rock masses or of an entire pillar cannot be ruled out, because the almost continuous rockfall activity causes a state of general instability of the entire rock mass.