The mechanism for fatigue crack growth in aluminum alloys under a chemically aggressive environment is discussed, based on the current understanding of hydrogen embrittlement phenomena. This mechanism is discussed quantitatively in terms of the three-term superposition model proposed by Wei et al. A diffusion-controlled model, characterizing the cycle-dependent interaction of fatigue loading and environmental attack, is developed, based on the assumption that crack growth enhancement results from microvoid nucleation due to hydrogen accumulation at inhomogencities ahead of a crack tip. This model is evaluated with limited data on Aluminum 7075-T6. The model developed in this paper accounts for the significant parameters affecting corrosion-fatigue crack growth enhancement. Integration of this model into the superposition scheme is discussed, including the application to predicting crack growth behavior in a corrosive environment for spectrum loading.