For the first time, this paper presents field computation results and performance of an axial-flux permanent magnet synchronous generator (AFPMSG) based on a time-stepping, 3-D finite-element analysis (3-D FEA). The prototype generator studied has a ferromagnetic outer rotor frame and a totally enclosed design, while a coreless stator armature configuration is used. Based on the machine geometry, a 3-D FEA model is developed in order to determine the principal field components. The flux in the rotor back plate and the transverse flux through the ferromagnetic spacer, which is part of the rotor frame, can both be predicted. A time-stepping, coupled field-circuit approach enables the waveforms and load characteristics of the AFPMSG to be obtained accurately. The computed results are validated by experiments on the prototype generator.