Guinea-race sorghums originated in the W.African Savanah.  They are critically important for food security and account for 50% of all sorghum produced in Africa.  This race is “rustic” with outstanding adaptation, plant heights of 3-5m, and total biomass yields up to 10 t/ha.  Grain yields, however, respond poorly to intensified production conditions. The challenge is to use the diversity within this race to increase yields while maintaining the adaptive characteristics.  An improved understanding of the structure of diversity within this race will enable more effective use of this germplasm for developing source populations, varieties and hybrid parents.  A Guinea-race core collection of 293 accessions was formed from the 3907 Guinea Accessions in the ICRISAT Sorghum Collection using principal components analysis with 9 quantitative traits (flowering dates, plant height, peduncle exertion, panicle width and length, grain size and seed weight).  This core collection was evaluated for key agronomic characteristics in Mali. Diversity was observed for all traits.  Plant heights ranged from 1.3 to 5.5m, panicle lengths from 20 to 61cm, and thousand grain weights from 4 to 36. No major differences were observed between geographic regions (Western and Central-, Eastern and Southern Africa, Asia) as most of the variation was within regions. Within regions some patterns of diversity appeared.  For example a higher frequency of accessions with large grain size were observed from Cameroon and Malawi.  To characterize the core collection for fertility reaction on A1 cytoplasm for hybrid parent development, a sub-set of 62 accessions were crossed onto male-sterile lines and the F₁s tested in Mali and Burkina Faso. Thirteen accessions showed maintainer reaction, 38 restorer reaction and the remainder showed predominantly partial fertility. Considerable plant-to-plant variability occurred within accessions. Whereas more than 40% of accessions from Burkina Faso and Senegal showed maintainer reaction, only restorer reactions were observed among accessions from Nigeria, Cameroon and Asia.  This initial characterization information suggests possible starting points for more detailed evaluations. Accessions with targeted traits, such as large grain size, could be used directly in variety and hybrid parent development, or introgressed into a newly created Dwarf Guinea-race random-mating population to establish trait specific source populations for targeted environmental zones.