Phase stability properties of fluid mixtures composed of hard sphere particles interacting via an attractive Yukawa tail are studied in the mean spherical approximation. The theory shows how the occurrence of either liquid-liquid or liquid-vapour spinodal decomposition correlates with the interparticle potential parameters and the density ρ* of the system. It appears that consolute-type decomposition is favoured at high ρ* or when the ‘unlike’ to ‘like’ interaction strength ratiovis small; by contrast, liquid-vapour type decomposition takes place at low ρ* or highvvalues. A numerical estimate of the threshold density separating the two regimes of phase stability is made on the basis of a very simple modelling of the interaction energies. An analysis is also made of theq→ 0 limit of the partial structure factorsSij(q), which gives an insight into the modifications occurring in the microscopic structural arrangement of the system at the ‘crossover’ point. Possible applications to real fluid mixtures are discussed.