The study took place in four French administrative depart-ments (Isère, Bas-Rhin, Haut-Rhin, Tarn), which were cov-ered by a population based cancer registry (part of an
international network of such registries). These registers
are complete for NHL as ascertained by the ratio of the
number of deaths to the number of cases registered during
1993–1997 (ranging from 39 to 50%, and from 42 to
69% among males and females, respectively), very similar
to those reported in other western countries [17]. Virtu-ally, all cases were histologically verified (98 to 99%). The
study area comprised a total of 2270 communities (census
block groups with a relatively homogenous population of
approximately 2000 inhabitants), used as statistical units.