Due to the change in environmental conditions, hygrothermal residual stresses may induce buckling and dynamic instability in composite shell structures. This paper investigates the vibration characteristics of pre- and post-buckled hygro-thermo-elastic laminated composite doubly curved shells. The geometrically nonlinear finite element method is used for the analysis. Both deep and shallow shell surfaces are modeled using an orthogonal curvilinear coordinate system. The mechanical linear, nonlinear stiffnesses, the hygrothermal nonlinear geometric stiffness and the hygrothermal load vector are presented. The arc-length method is implemented to capture the snapping behavior of the structures under hygrothermal environmental conditions. Numerical results of nonlinear deflections and fundamental frequencies along with the deflection shapes and the mode shapes are presented and discussed for spherical and cylindrical shell panels. The fundamental frequency decreases in the pre-buckling region and increases in the post-buckling domain of the snap-through process. It is also noted that as the thickness of the panel decreases, the limit point load for buckling decreases: if the radius of curvature increases, the fundamental frequency decreases under a uniform hygral condition. The "curve veering phenomena" is observed for spherical panel under thermal load. The geometrically nonlinear deflection behavior affects the vibration characteristics in a hygrothermal environment. (C) 2009 Elsevier Ltd. All rights reserved.