The development, validation and application of the Swiss-SEP index consisted of the following five steps: (1) the definition of neighbourhoods, with moving boundaries, around each of the 1.27 million buildings recorded in the 2000 census; (2) the characterisation of the socioeconomic standing of these neighbourhoods based on median rent, education and occupation of household heads and household crowding; (3) the construction of the index by combining the loadings of the first component from principle component analysis (PCA); (4) the validation of the index using independent data on the financial situation of households and (5) the analysis of associations between the Swiss-SEP index and all-cause and cause-specific mortality in the adult population resident in Switzerland.