Communication: Hyperbranched aliphatic copolyesters have been prepared by copolymerization of c-caprolactone with 2,2-bis(hydroxymethyl)butyric acid, catalyzed by immobilized Lipase B from Candida antarctica (Novozyme 435) under mild conditions. Via this novel combination of ring-opening AB polymerization and AB(2) polycondensation, the degree of branching (DB) and, consequently, the density of functional end groups can be controlled by the comonomer ratio in the feed (0 < DB < 0.33).