The implementation of an antenatal screening programme for neonatal alloimmune thrombocytopenia (NAIT) is currently under debate. We evaluated the detection rate for NAIT in a nonscreened population of 661 200 births where NAIT was diagnosed on clinical indication. We did a cross-sectional comparison with a population of 100 448 human platelet antigen 1a (HPA1a)-screened pregnancies from three of the five health regions in Norway. In a nonscreening situation, 7.5 cases of NAIT were detected per year compared with 53 cases when screening was applied. The detection rate of NAIT in Norway was therefore 14% of the expected rate.