Small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), and dynamic light scattering (DLS) are used to study the temperature dependence of asphaltene aggregate sizes in toluene solutions. A large range of aggregate sizes is covered by combining the three scattering methods. The effect of temperature on aggregate size is also investigated over a considerable temperature range. A huge modification of asphaltene macrostructure is observed. At high temperatures, reversible aggregation of asphaltene leads to stable small entities. When decreasing the temperature, irreversible aggregation of asphaltene occurs, corresponding to a large increase of the aggregate size. We have also investigated the effect of pressure on asphaltene solution in toluene as a function of temperature. Our results indicate that pressure has a minor effect, which is much less important than that of temperature, on the weight of the asphaltene aggregates.