A comparative study of the sintering and grain growth of 3 mol% yttria zirconia using conventional and microwave heating was performed, Extensive measurements of grain size were performed at various stages of densification, and following isothermal ageing at 1500°C for 1, 5, 10 and 15 h. Microwave heating was found to enhance densification processes during constant rate heating. The grain size/density relationship for the microwave-sintered samples was shifted in the direction of increased density for density values less than 96% of the theoretical value when compared to conventionally heated samples. This suggests that there may be a difference in the predominant diffusion mechanisms operating during the initial and intermediate stages of sintering. Results of the ageing experiments showed that once densification was near completion, grain growth was accelerated in the microwave field, and exaggerated grain growth occurred. © 1996 Chapman & Hall.