We present a theory of spinodal decomposition which is based on the linearized hydrodynamic equations including the stochastic fluctuations in stress tensor and heat flux and which accounts for nonlocal driving force through pressure gradient. The equation of state is obtained using liquid-state perturbation theory, and the transport coefficients are obtained from the Enskog theory of dense fluids. The theory thus has no adjustable parameters. The time-dependent structure factor calculated from the theory is in good quantitative agreement with molecular-dynamics experiments for early times. An effective amplification factor extracted from the experimental results also agrees well with the theoretical dispersion of the growing mode. Extension of our theory to binary-fluid mixtures shows that, within the linear regime, hydrodynamic flow effects are negligible and the Cahn-Cook description is adequate. © 1982 The American Physical Society.