The possibility of the existence of fullerenes in organic solvents in the form of clusters containing a number of fullerene molecules is discussed. A theory is developed on the basis of a droplet model for clusters, which enables one to describe the distribution function of clusters by size and to obtain the non-monotone temperature dependency of fullerene solubility observed recently. It is shown that a phase transition taking place in a crystalline C-60 at T-c similar or equal to 260 K significantly changes the role of clusters in solution. At T > T-c the distribution function of clusters, characterized by the number n of constituent molecules, has its maximum at n* = 11 and higher, while at T < T-c the value of n* similar or equal to 3-5. This is the reason for the different temperature dependencies of fullerene solubility in various temperature ranges. Comparison of the calculated values of solubility with experimental data permits one to obtain energetic parameters characterizing the interaction of a fullerene molecule with its surrounding in a solid phase or a solution.