Perinatal mortality is a major constraint in African sheep-farming systems 1. Though sheep is an important animal production in Senegal (4.3 106 heads in 1999, FAO estimate), few information is available on this topic. As a part of a broader study on sheep-farming systems in Senegal, a prospective survey was conducted to assess lambs perinatal mortality in 2 extensive systems. Because nutrition was a limiting factor for sheep productivity, 3 nutritional risk factors were evaluated: ewes bodycondition score at lambing (BCS), ewes-postpartum weight (PPW) and litter size.