During the period 1986-1988, approximately 1,200,000 portions of blood were anti-HIV screened in Denmark. A total of 19 donors were found to be anti-HIV positive and no increase in the frequency of anti-HIV blood donors has been observed during this period. At a subsequent interview, nine out of these 19 donors (47%) were shown to have risk factors for HIV infection. During the same period, a total of 12 cases of transfusion-associated HIV infection were found at follow-up control of recipients of blood from previous donations from donors demonstrated to be positive after 1986. Four of the cases were demonstrated to be positive by blood donor screening and eight in other ways. Finally, five cases of transfusion-associated HIV infection in recipients have been reported where no positive donor could be identified. One case of HIV infection could be attributed to transfusion with screened anti-HIV negative blood. On the basis of information from blood donor screening, it is concluded that the risk that a screened anti-HIV negative blood portion in Denmark can transmit HIV infection is less than one per 400,000.