This study defined the incidence, clinical and haematological characteristics of infantile pyknocytosis in a monocentric retrospective study of 149 blood samples referred for unexplained neonatal haemolytic anaemia. Pyknocytosis was diagnosed in 14 patients (9·4%). All patients had neonatal jaundice and severe anaemia (mean nadir haemoglobin: 6·8 g/dl) at a mean age of 21 d. The percentage of pyknocytes was 4–23%. Packed red blood cell transfusions were needed in 11 of 14 patients. Haemoglobin levels reached normal values within a mean time of 4 months. Infantile pyknocytosis is an unusual cause of neonatal haemolytic anaemia, which requires careful examination of blood smears.