The results reported herein demonstrate that the chemoselectivity (S(H)2 ring opening vs abstraction of a cyclopropyl hydrogen) associated with the free radical chlorination of cyclopropane is solvent dependent. Internal pressure is implicated as the solvent parameter responsible for the observed solvent effect. (Solvents of high internal pressure favor the S(H)2 process; hydrogen abstraction becomes more important in solvents of low internal pressure or in the gas phase.) Extrapolation of the solution phase results to zero internal pressure accurately predicts the gas-phase result, suggesting that the difference in chemoselectivity between the vapor- and condensed-phase reactions is attributable to internal pressure in the condensed phase medium. No evidence for the chlorine atom cage effect is found in the chlorination of cyclopropane.