[The municipal register as a source of controls]

One of the main problems in selecting a control group in community based case-control studies is the availability of an appropriate source of the same geographical area. In Spain, the Municipal roll consists on a list of inhabitants being a potential source to obtain representative samples of general population. The structure of the Municipal roll is described with its contents in districts and census tracts. The strategy of the Municipal roll utilization in performing a childhood leukemia case-control study is also described. Its limitations are compared with those founded in the methods used currently in other countries like random digit dialing and birth certificates. Finally and given the current structure of the spanish Municipal roll, we discuss the usefulness of different approaches to obtain a random sample from this source and the problems which arose from using a method of matching by municipality, which is a cheap and quick procedure.