We report a case of dramatic outcome of severe hemolytic disease in a newborn due to RH1 incompatibility. A newborn with A RH1 blood group was admitted in the Mohammed V Military Teaching Hospital for the problem of hydrops fetalis associated with RH1 incompatibility. The blood group of his mother, aged 31, was AB RH1-negative and that of his 37 year old father was A RH1. The mother had a history of 4 term deliveries, 3 abortions, and 1 living child. There was no prevention by anti-D immunoglobulin postpartum. The mother's irregular agglutinin test was positive and the pregnancy was poorly monitored. The laboratory tests of the newborn showed a high total serum bilirubin level (30 mg/L) and macrocytic regenerative anemia (Hemoglobin=4 g/dL, mean corpuscular volume = 183 fL, reticulocytes count =176600/m3). The blood smear showed 1256 erythroblasts per 100 leukocytes, Howell-Jolly bodies and many macrocytes. The direct antiglobulin test was positive. He was transfused with red blood cell concentrates and treated with conventional phototherapy. The evolution was unfavourable; he died three days after the death of his mother. The monitoring of these high-risk pregnancies requires specialized centers and a close collaboration between the gynaecologist and the blood transfusion specialist to strengthen the prevention, as well as clinico-biological monitoring in patients with a history of RH1 fetomaternal alloimunization.