An analysis is made of film condensation on a vertical fin which is attached to a cooled vertical plate or cylinder. This is a three-dimensional problem in which the condensation process on the fin surface is tightly coupled to conduction within the fin. A physically meaningful similarity solution of the problem was formulated and numerically evaluated. Beyond the range where the similarity solution is valid, a finite-difference marching solution of the governing partial differential equations was carried out. The heat transfer results from the similarity solution, which are represented by simple algebraic formulas, appear to be applicable for the operating range encountered in practice. It was found that the calculated fin heat transfer is markedly less than that which would be predicted by an isothermal fin model, so that the use of such a model substantially overestimates the performance of the fin.