The Bristol Royal Infirmary is located on the south-easterly face of Kingsdown Hill overlooking the centre of Bristol. A series of extensions to the Infirmary have been constructed since 1966 and are planned for the future. The hill is underlain by alternating hard sandstones and mudstones of the Quartzitic Sandstone Group which dip towards the south-east at a steeper angle than the ground slope. The Carboniferous rocks are overlain by the Triassic Dolomitic Conglomerate in the upper part of the site, and by Triassic marls and fill at lower elevations. The hillside has a past record of instability both in superficial materials and in bedrock. The stability of the site had to be judged both overall and in relation to the design and construction of individual structures. The design of the foundations for each of these structures was based upon drilling coupled with a programme of laboratory and in situ tests. The largest building is the Outpatients Department which required major basements involving deep excavation into the hillside undercutting the bedding. The foundations for this structure were primarily created by buttresses formed in trench and combined with cross walls so ensuring total stability at all stages of excavation. In contrast, the Radiotherapy Centre is mainly founded on isolated bases carried down to bedrock and appropriately stepped in level. The thick walls between the treatment rooms in the basement were keyed into the quartzitic sandstone or very firm mudstone. The Maternity Hospital, located at the top of the site on thick Triassic deposits, has been founded on large diameter bored piles drilled into the Dolomitic Conglomerate. Attention is drawn to the special problems which arose during construction including the need for controlled blasting for excavation and the control of water, partly in relation to a medieval tunnel system.