Seed loss from sesame capsules before harvest is a major economic problem for mechanized production. Capsule dehiscence and seed loss were investigated by examining capsule anatomy of 32 sesame varieties and relating anatomical features to a measure of seed retention. This survey of sesame capsule anatomy illustrated that differences between varieties were mostly quantitative, except for the presence of cell layers over the median vascular bundle. This feature, associated with the indehiscent (idid) genotype, prevented capsule-splitting and increased seed retention. None of the dehiscent sesame varieties had capsule anatomical features that were correlated with seed retention. During capsule senescence, mesocarp cells shrank more than endocarp cells creating tension in the drying capsule wall. The tension forced capsules open along a zone of weakness between locules.