We present stratigraphical and stable isotope data (δ13C, δ18O) for two successions selected from the K–T boundary succession seen in the cliff sections of Stevns Klint (Denmark). Although the succession at Højerup is well known from other studies, that at Kulstirenden has not been described before. It contains an exceptionally thick (c. 40 cm) development of the boundary clay (or Fish Clay), which includes the ‘red layer’ just above its base. There is clear evidence of shallowing in the latest Maastrichtian in advance of the K–T boundary, together with fluctuations in sea-water temperature. The detailed δ13C record at Kulstirenden provides a record of the environmental changes within the boundary interval with a resolution better than many other successions described in the literature.