Why does a greater proportion of the population of northern Sweden suffer from such diseases as diabetes, stomach cancer and those of the circulatory system than people living in the southern part of the country? Are there any environmental factors that can explain these circumstances? It can be concluded from this study that the regional mortality pattern displayed here cannot be disregarded. The consistency of the finding is supported by the joint analysis of several data sources. The analyses in this study indicate that dietary habits, water hardness, and seasonal variations--rather than smoking habits or alcohol abuse--could be causal explanations for the regional mortality pattern in circulatory diseases. Diet and genetic factors may explain the regional variations in diabetes, while there is so far no evidence for associations between stomach cancer and any environmental factors. Thus, there is no correlation between stomach cancer and waterborne nitrate level in the 24 Swedish counties. This calls for further studies on the connections between stomach cancer and intake of salt, vitamins or trace elements. The preparation of foods could also have some impact on the incidence of stomach cancer.