Infection is one of the leading causes of mortality in thalassemia patients. This study aimed to examine qualitative and quantitative changes in monocytes in thalassemia patients. Monocytes were isolated from peripheral blood mononuclear cells and separated into subpopulations by flow cytometry. Cytokine levels were measured using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and sandwich enzyme-linked immunosorbent assay (ELISA). The primary endpoint was monocyte-derived TNF-α expression. A total of 78 patients and 26 controls were included. The mean log (TNF-α fold-change) by qRT-PCR was significantly lower in all thalassemia groups, at 1.27 in controls, versus 0.97 (p = 0.0014) in non-transfusion-dependent thalassemia (NTDT), 0.96 (p = 0.0004) in non-splenectomized transfusion-dependent thalassemia (TDT-NS), and 0.87 (p < 0.0001) in splenectomized transfusion-dependent thalassemia (TDT-S). Similarly, the mean 2-h TNF-α level measured by sandwich ELISA assay was significantly lower in all thalassemia groups, at 98.16 pg/mL in controls, versus 56.45 pg/mL (p = 0.0093) in NTDT, 39.05 pg/mL (p = 0.0001) in TDT-NS and 32.37 pg/mL (p < 0.0001) in TDT-S. Likewise, TDT patients had a significantly decreased percentage of non-classical monocytes, by approximately half compared to controls. Our results show that thalassemia major patients have clearly impaired monocyte counts and function.