Beta-thalassaemia minor and iron deficiency are the most common causes of microcytosis and/or hypochromasia. The present study evaluates the diagnostic reliability of different RBC indices and formulas, as well as our proposed formula, in the differentiation of the beta-thalassaemia minor from iron deficiency in Palestinian population. Complete blood count (CBC) parameters of 2196 certainly diagnosed (1272 beta-thalassaemia minor and 924 iron deficiency) samples were used to evaluate the following indices and formulas: Bessman index (RDW), Mentzer formula (MCV/RBC), England and Fraser formula (MCV - RBC - 5 x Hb- 3.4), Shine and Lal formula (MCV2 x MCH/100), Ehsani formula (MCV-10 x RBC), Srivastava formula (MCH/RBC), Green and King formula (MCV2 x RDW/Hb x 100), red distribution width index RDWI (RDW x MCV/RBC), RDW/RBC, as well as our formula (MCV-RBC -3 x Hb). For each index and formula, the receiver operative characteristic (ROC) curve was constructed to calculate the area under the curve (AUC), in addition, sensitivity, specificity, and likelihood ratios were calculated. No significant differences were reported between our formula, Green-King formula and the RDWI (P > 0.05) in discriminating beta-thalassaemia minor from iron deficiency (AUC = 0.914, 0.909 and 0.907 respectively). However, the three indices and formula showed the highest efficiencies and they were significantly (P < 0.05) better than the others in the discrimination efficiency . It was concluded that our formula, Green-King formula and the RDWI provided the highest reliabilities in differentiating beta-thalassaemia minor from iron deficiency in Palestinian population while Bessman index was poor and ineffective for that purpose.