This study was undertaken to evaluate the major causes of mortality at different stages of incubation and their economic impact in response to sustainability challenges at the Rwandan National Hatchery. Methods: The study evaluated the fertility, hatchability and embryonic deaths in broiler-producing flocks (B series) and layer-producing flocks (L series) at Rubilizi, a state-owned hatchery in Kigali, Rwanda. Results: Mean fertility in the B series (94.23%) was not significantly different (P >

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... .05) from that of the L series (93.24%). Mean hatchability in the B series (57.39%) was significantly (P < 0.05) higher than that of the L series (42.2%). Early embryonic deaths in the L series (8.6%) were significantly (P<0.05) higher than those in the B series (3.9%). Middle embryonic deaths in the L series (6.2%) were significantly (P < 0.05) higher than those in the B series (1.8%). Late embryonic deaths in the L series (21.6%) were significantly higher (P < 0.05) than those encountered in the B series (13.0%). The occurrence of hatch debris in the L series (34.14%) was significantly (P<0.05) higher than that in the B series (24.42%). There was no significant difference in the proportions of pips, rots and malformations/malpositions between the B and the L series (P > 0.05). Conclusions: Low hatchability in the L series possibly resulted from the higher number of embryonic deaths and hatch debris and not from reduced fertility or cull chicks. Total chick losses during the study amounted to US$54 327.00. The hatchery was experiencing more losses in layers than in broilers as emanating from low hatchability of the layers. Further investigations are needed with aim to maximise the hatchery's capacity.