In this paper, the shear-lag in a thin-walled cantilever pipe is discussed, utilizing the author's fundamental differential equation in a single displacement for a thin cylindrical shell. The results are compared with those obtained by the simple beam theory or modified beam theory. The deflection at the loaded side is very close to that estimated by the modified beam theory, while the configuration of the elastic line and the stress distribution near the fixed side are fairly different from those presumed by such a beam theory.