Formation of microstructure in homogeneous associated liquids is analysed through the densitydensity pair correlation functions, both in direct and reciprocal space, as well as an effective local one-body density function. This is illustrated through a molecular dynamics study of two neat alcohols, namely methanol and tert-butanol, which have a rich microstructure: chain-like molecular association for the former and micelle-like for the latter. The relation to hydrogen bonding interaction is demonstrated. The apparent failure to find microstructure in water -a stronger hydrogen bonding liquid-with the same tools, is discussed.Liquids are generally thought as macroscopically homogeneous when they are considered far from phase transitions and interfacial regions. From a statistical mechanical point of view, homogeneity is expressed by the fact that the order parameter, in this case the one body density, which formally depends on both the position and orientation of a single particle 1 (as in a crystal or a liquid crystal, for example), is a constant throughout the sample: ρ (1) (1) = ρ = N/V , where N is the number of particles per volume V. As a consequence, the microscopic description of the structure of a neat liquid starts from the two-body density function ρ (2) (1, 2) = ρ (1) (1)ρ (1) (2)g(1, 2) that expresses the density correlations between particles 1 and 2, and reduces in this case to ρ 2 g(1, 2) , where g(1, 2) is the pair distribution function. Associated liquids, such as water and alcohols, for example, belong to a special class because of the particularity of the hydrogen bonding (HB) that is highly directional, and tend to enhance the structure the liquid locally. One particularly interesting example of this phenomena is the microheterogeneous nature of aqueous mixtures, which has attracted a recent upsurge of interest [1,2,3,4,5,6,7]. Perhaps the most remarkable reported fact is that watermethanol mixtures show local immiscibility at microscopic level, while being miscible at macroscopic level [1,2]. In order to appreciate this result it is interesting to compare it to microemulsions where bicontinuous phases are usually observed, and micro-immiscibility operates with domain sizes ranging from 100 nanometers to few micrometers, while those mentioned here are around few nanometers-that is about few molecular diameters. In addition, it is important to note that bicontinuous phases in microemulsions arise after a phase transition has occurred from disordered to ordered phase; while in the former case, we are still in a genuinely homogeneous and disordered liquid phase. From these facts, microheterogeneity in aqueous mixtures can be considered as both obvious and mysterious, obvious because the mechanism behind it is the strong directionality of the hydrogen bonding, and mysterious because of the existence of stable microimmiscibility of water and solute in a macroscopically homogeneous sample. In contrast to the situation for mixtures, neat water do not seem to exhibit any micro phase separation betwe...