Medical geology, a sub-field of geology, is closely linked to environmental epidemiology. The focus of the geomedical studies is on the natural geological environment in relation to the distribution of health problems among humans and animals. Several medical geology studies have been performed at GTK during recent decades and three of them are summarized in the present article. It is important to understand the geographical variation of certain chronic disease occurrences when generating hypotheses regarding potential natural environmental risk factors for the disease in question. The results of the SPAT project (Development and application of new methods for determining the geographical variation of health phenomena in Finland, 1998-2000, and Geographical variation of non-communicable diseases, 2002-2004) showed that high water hardness, especially high Mg concentrations in local ground water, was geographically associated with a lower incidence of acute myocardial infarction. The health risk assessment of the RAMAS project (Risk assessment and risk management procedure for arsenic in the Tampere region, 2004-2007) showed health risks if arsenic-rich water from drilled bedrock wells was used as drinking water. The study implied an increased incidence of some typically As-induced cancers in the study population with a potential long-term exposure to drinking water containing As. The results from a sulphide-rich bedrock area in eastern Finland indicated that the use of dug well water, as well as the consumption of local potatoes and mushrooms, slightly increased the Hg concentration in the hair of local residents in areas with elevated Hg concentrations in bedrock. However, the most important route of Hg to humans was via the consumption of fish, and the methyl-mercury content of the fish was not originally derived from bedrock but was rather related to lakes located in topographic depressions with large catchment areas. Hg concentrations in the muscle of noble crayfish (Astacus astacus L.) were also higher on average in lakes located in topographic depressions. In Finland, geographical variation in the occurrence of certain chronic diseases has remained relatively stable for decades, which warrants further studies from the viewpoint of medical geology. Close co-operation between geoscientists, health scientists and statisticians will also be necessary in future multidisciplinary medical geology studies.