We study the asymptotic behaviour of the solution of linear and nonlinear e
lliptic problems in cylindrical domains becoming unbounded in one or severa
l directions. In particular, we give estimates of the difference between th
e solution in bounded domains and its limit in terms of the size l of the d
irections going to infinity. (C) 2000 Academie des sciences/Editions scient
ifiques et medicales Elsevier SAS.