Asphaltene molecular size and weight have been of concern since asphaltenes were first isolated from crude oils. Despite previous divergent results on this topic, in recent years, there has been a growing consensus among all mass spectral ionization techniques and all diffusion measurements that asphaltenes are fairly small molecules. In this paper, fluorescence correlation spectroscopy (FCS) is used to determine translational diffusion coefficients of asphaltene and model compounds under a variety of conditions. These FCS studies provide several stringent tests on asphaltene molecular size and architecture. A broad range of concentrations including ultralow concentrations is investigated to ensure the lack of potential aggregation difficulties. Large temperature variations are used to test the application of the simple diffusion equation. FCS results here clearly show the dependence of the diffusion constant on the molecular weight. Finally, FCS results on asphaltenes are in quantitative agreement with those of time-resolved fluorescence depolarization on asphaltenes. A comparison of the results herein with previous FCS and time-resolved fluorescence depolarization (TRFD) results on the same asphaltenes confirms the correlation between molecular size and asphaltene chrornophore size; this supports a molecular architecture with one or two polycyclic aromatic hydrocarbons (PAHs) per molecule and counters proposed structures with many PAHs per asphaltene molecule.