New measurements have been made of rate constants for electron attachment to c-C4F8 (octafluorocyclobutane) and thermal electron detachment from the parent anion, c-C4F8-, over the temperature range 298-400 K in 133 Pa of He gas in a flowing-afterglow Langmuir-probe apparatus. From these data the electron affinity for c-C4F8 was determined, EA(c-C4F8)=0.63+/-0.05 eV. The motivation was to resolve a discrepancy between our earlier EA estimate and a higher value (EA=1.05+/-0.10 eV) reported from a recent experiment of Hiraoka [J. Chem. Phys. 116, 7574 (2002)]. The electron attachment rate constant is 9.3+/-3.0x10(-9) cm(3) s(-1) at 298 K. The electron detachment rate constant is negligible at room temperature but climbs to 1945+/-680 s(-1) at 400 K. G3(MP2) calculations were carried out for the neutral (D-2d, (1)A(1)) and anion (D-4h, (2)A(2u)) and yielded EA(c-C4F8-)=0.595 eV. Bond energies were also calculated for loss of F from c-C4F8 and loss of F or F- from c-C4F8-. From these, dissociative electron attachment is found to be endothermic by at least 1.55 eV. (C) 2004 American Institute of Physics.