Based on c. 1500 km reflection seismic profiles, the Quaternary formations and their pre‐Quaternary substratum in the southeastern Kattegat are described and a geological interpretation is suggested. The major volume of Quaternary deposits is found in a broad north‐northwest south‐southeast trending topographic depression. The substratum consists of Upper Cretaceous limestone in the region north of the Sorgenfrei–Tornquist Zone, and inside this zone older Mesozoic sedimentary rocks and Precambrian crystalline rocks are found. The Quaternary is divided into four seismic units. No direct stratigraphic control is available, but the units are assumed to represent a period ranging from Late Saalian to Holocene. The oldest unit (unit 3) is composed of deposits of supposed Late Saalian to Middle Weichselian age. This unit was severely eroded probably by the Late Weichselian ice sheets in a zone extending 40–50 km from the Swedish coast. Unit 2 represents the Late Weichselian till deposits. North and east of the island of Anholt unit 3 is cut by a system of channels eroded by glacial meltwater. By the erosion a relief up to c. 100 m was formed. After the recession of the Late Weichselian ice, an up to 100 m thick sequence of water‐lain sediments (unit 1) was deposited in the erosional basin and channels. Holocene deposits (unit 0) of considerable thickness have only been identified in the channels in the northern part of the area.