A general method of analysis based on random variable transformations technique is presented for studying stochastic normal deflection of composite plates. A simply supported orthotropic rectangular thin plate model with indeterminate elastic coefficients is investigated to obtain the marginal density function of its maximum normal deflection under a uniform load. A general closed form marginal density function of the maximum normal deflection is obtained. The method of analysis is illustrated through studying different cases for the distributions of the considered stochastic variables. A numerical study of the uniform distribution case is performed.