The state of Minas Gerais has the third largest population of hemophilia A (HA) patients in Brazil. Fundação Hemominas is the treatment center of reference in the state for clinical and laboratory care of HA patients. Patients are classified according to residual plasma FVIII activity (FVIII:C): Patients with FVIII:C 5%-40% are classified as mild HA; FVIII:C of 1%-5% are classified as moderate HA; and patients with FVIII:C <1% are classified as severe HA. Patients with severe HA often have inversions of introns 1 and 22 in the FVIII gene. The aim of this study was to diagnose inversions of introns 1 and 22 patients with severe and moderate HA. For this purpose, peripheral blood samples were collected from 39 male patients, median (MED) age was 31 years (IQR 19 -42 years), classified as severe (27 patients) or moderate (12 patients) with FVIII:C dosage <3%. After collection, samples were processed for genomic DNA extraction. First, patients were genotyped for intron 22 inversion by inverse PCR. Patients who were negative for intron 22 inversion were genotyped for intron 1 inversion. Samples negative for both inversions will be full-length NGS sequencing. Among 39 patients, 21 (54%) were diagnosed with intron 22 inversion and one (2%) with intron 1 inversion. In addition, among 12 patients previously diagnosed with moderate HA, seven (58%) patients were reclassified as severe HA because they presented intron 22 inversion. The molecular diagnosis proved to be important for the correct classification of the severity of HA patients. Due to the diagnosis normally based only on residual activity of plasmatic FVIII, the disease severity classification may be incorrect. It is believed that the high variability of coagulometric techniques and the treatment of patients prior to laboratory diagnosis may affect the correct classification of HA patient severity. This is an ongoing study and the number of participants needs to be increased in order to draw conclusions. We thank all participants, Fapemig, Hemominas, and the CGSH of the Ministry of Health.