Packed red blood cell transfusion is a common intervention in the treatment of anaemia in children. The adequacy of the volume of blood transfused is usually determined by doing a post-transfusion haematocrit check. None of the existing formulae used in estimating the required volume of packed red blood cells can precisely predict the post-transfusion haematocrit level, underscoring the need for this check. Doing this test at the appropriate time will enhance optimal patient care. Haematocrit is generally considered to stabilize 24 hours after transfusion, with little supporting evidence. While there is yet to be a consensus on the optimal time to do post-transfusion haematocrit check, available studies though sparse, have shown that final haematocrit stabilization occurs much earlier in neonates, older children and adults. In Nigeria, the timing of this test as practised in different centres, ranges from six to 72 hours with limited evidence, especially in postneonatal children. A prospective cohort study was conducted aimed at determining the optimal time for haematocrit check after packed red blood cell transfusion among infants and children aged 29 days to 15 years old at National Hospital Abuja. Subjects who required packed red blood cell transfusion and without evidence of ongoing loss of red blood cells were recruited for the study. Relevant history, physical findings and laboratory results were documented for each subject. The volume of packed red blood cells required for transfusion was calculated based on the unit policy – [Desired Increment in Haemoglobin Concentration x Weight (kg) x 4]. A capillary blood sample was obtained from each subject just before the commencement of transfusion. Serial capillary blood samples were obtained at one, six, 12, 24 and 48 hours after completion of transfusion.