Differential scanning calorimetry has been used to study the melting and the low-temperature transitions of tetrafluoroethylene-perfluoroalkylvinylether copolymers (PFA). Melting is similar to that of PTFE in that it is subject to superheating, moreover the melt-crystallized samples show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal-crystal transitions are observed for copolymers containing 2 mol % of perfluoromethyl-, perfluoroethyl-, and perfluoro-n -propylvinylether. In the case of perfluoromethylvinylether as a comonomer, low-temperature transitions are present only up to a content of 4 mol %. The effect on melting and low-temperature transitions of both the comonomer content and of the type of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonomer concentration and have been found to be independent on the chemical nature of the side group.