A model is presented that describes the clustering of microemulsion droplets from a thermodynamic point of view. It is based on two assumptions: one assumption is that the microemulsion droplets aggregate linearly. The other assumption is that the chemical potential per droplet is equal for all sizes of aggregates. By means of the fundamental thermodynamic equations of self-association the distribution of aggregates can then be calculated. The predictions of this model are in agreement with the available experimental data.