Serial sectioning and computer-aided visualization of three-dimensional reconstructions were used to reveal the three-dimensional morphology, connectivity and distribution of proeutectoid cementite precipitates in a model Fe–1.34% C–13.0% Mn alloy. Only dendritic grain boundary precipitates and Widmanstätten precipitate morphologies were observed in the present alloy. Unlike earlier morphological studies of similar alloys, intragranular precipitates were not observed. Scanning and transmission electron microscopy of deeply etched specimens corroborated and augmented these results. Three-dimensional analysis has also made possible the first quantitative three-dimensional measurements of cementite precipitates and yielded a more precise classification of cementite precipitates than was possible with classical two-dimensional techniques.