Molecular dynamics simulations were used to predict the thermodynamical properties of the hydration process of the adamantane, diamantane, and trimantane, the first three members of the series of diamondoids. Free energy results suggest that the water solubility of these molecules is low. The hydration free energy increases with size of the diamondoid. As for the alkane hydrocarbons, hydration free energy correlates linearly with the surface accessible solvent area; however; here it has been shown that small diamondoids present hydration free energy significantly lower than the n-alkanes of similar molecular weights. The decomposition of the hydration free energy in enthalpic and entropic terms revealed that the hydration process of the small diamondoids is entropic driven. The potential of mean force calculations indicates that the aggregation of these species in the aqueous occur spontaneously and that the contribution of the solvent is greater the larger the diamondoid.