The Lake Vättern area in Southern Sweden has been studied by gravity methods in an attempt to secure new information about the lake as a “graben” structure. An interpretation of the main anomalies shows different relationships between the “tectonic” near-surface structures and the more deep-seated structures in the crust. Anomalies in precambrian granites and basic bodies outside the main area have also been interpreted to show the complexity of the earth's outer crust in these areas. The result of this investigation is that the graben structure is a very plausible explanation of the gravity anomalies. The Visingsö series is about 400 m thick in the southern part of the area but reaches a thickness of 1000–2000 m in the middle part. The thickness of the granites varies from about 15 km under the “graben” to some kilometres outside this area.