Over a 16 month period 307 children with suspected tuberculosis (TB) and an available full blood count (FBC) seen at Tygerberg Hospital in South Africa were evaluated and categorized as confirmed (A), probable (B), and no TB (C) according to WHO criteria. There was no difference in the mean age of the 168 group A (33.6 months), 83 group B (34.4 months), and the 56 group C (31.6 months) children. A lower mean haemoglobin (Hb 10.2 vs. 10.8 g/dl) was the only significantly different haematological parameter in children with TB compared with the comparison group (Group C). There were no differences in median total white cell count, neutrophils, lymphocytes, monocytes, platelets, or the proportion of children in each group with anaemia, microcytosis, neutrophilia, neutropenia, lymphocytosis, lymphopenia, monocytosis, thrombocytosis or thrombocytopenia. The most common haematological abnormalities in children with TB were the presence of anaemia, neutrophilia, and monocytosis but these changes were found with equal frequency in control patients. Although haematological abnormalities are fairly common in children with TB, in a developing country these abnormalities also occur frequently in children with other non-tuberculosis respiratory infections. An FBC has no diagnostic predictive value when investigating a child for TB.