We report a theoretical study of the unperturbed state of dendrimers, which is realized when the second virial coefficient becomes equal to zero. This condition is achieved through a vanishing of the intermolecular free energy, which is obtained by mutual compensation of the two- and three-body interactions between two molecules. This procedure, which permits us to determine the Theta temperature of dendrimers as a function of their generation, is coupled to the problem of the intramolecular conformation, determined by minimization of the intramolecular free energy. The latter accounts for the two- and three-body interactions within the molecule, and for the configurational entropy. We find that the Theta temperature is a decreasing function of the dendrimer generation g, the decrease becoming relatively fast at large g, but is almost independent of the number of segments (one or two in our case) between adjacent branch points. At the Theta temperature, the residual three-body interactions within the molecule not compensated by the two-body attractions induce a significant swelling over the random-walk conformation for g >2.