The geometrically nonlinear problem of deformation of a cylindrical shell subjected to nonaxisymmetrical external pressure is considered. The initial problem is reduced to a one-dimensional boundary problem for a system of nonlinear differential equations, whose solution is constructed by the method of transition to a Cauchy problem. To investigate the behavior of the solution, the theory of branching-out of the solutions of nonlinear boundary problems is utilized. A numerical investigation of deformation of the cylindrical shell with a stepwise variation of the external pressure around the circumference is carried out. The main types of deformation of specific features of behavior are singled out: monotonous deformation, ″popping-out″ , general and local bulging.