The study included 50 cases with this disease which were divided into 2 groups: above and under 2,500 g. A relationship was established among weight and bleeding site, type of delivery, prothrombin activity and lethality. It was found that those under 2,500 g. bled earlier than those above 2,500 g. With higher percentage, the bleeding site was the digestive tract in both groups. Most of both groups bled between the 2nd and 6th day and a group of special interest was made up of 8 patients who bled between the 10th and 28th day of life and that we included as hemorrhagic disease of the newborn because bleeding appeared within the neonatal stage; these patients fell within the group showing the lowest prothombin activity. Bleeding within the central nervous system was frequent and showed the highest lethality.