Paroxysmal Nocturnal Hemoglobinuria (PNH) is a disease resulting from a somatic mutation in the PIG-A gene (phosphatidylinositol glycan class A), which encodes an anchor enzyme called GPI (glycosyl-phosphatidylinositol). The alteration in the synthesis of this enzyme leads to partial or total deficiency in anchoring certain proteins to the cell membrane, such as CD55 and CD59, resulting in the development of chronic intravascular hemolysis due to the increased sensitivity of GPI-deficient red blood cells to complement system attack. PNH can appear at any age, predominantly affecting adults between 20 and 40 years old. Its prevalence is estimated at approximately 38 per million individuals, and its incidence ranges from 0.08 to 0.57 per 100,000 person-years worldwide, thus considered a rare disease and, as such, challenging to diagnose. Flow cytometry-based PNH testing is the gold standard for diagnostic assistance, as it employs multiple monoclonal antibodies and a special reagent called Fluorescently Labeled Aerolysin (FLAER) capable of directly binding to the GPI-anchored protein and evaluating its expression with high sensitivity and specificity. PNH erythrocytes are divided into three clones based on the degree of expression of GPI-anchored proteins. A total of 1000 PNH under suspicion sample results were evaluated using flow cytometry at the Hermes Pardini Institute. The aim was to conduct an epidemiological survey of positive cases, as the laboratory receives samples from all over Brazil and there are few reports on this profile in South America. Additionally, a correlation analysis between positive results and other laboratory tests was conducted. The samples evaluated were collected between July 2022 and July 2023. We found a positivity rate of approximately 9.2%, and the age of positive patients ranged from 8 to 78 years old. Patients were stratified by age group and gender, and the results of associated tests were compiled. Our data align with findings in the literature, with women (55%) and individuals aged 31-40 years (21%) being the majority. However, it was noteworthy to observe a significant percentage of positive PNH cases among individuals under 20 years (12%) and over 60 years (23%). Abnormalities in other tests mainly occurred in hemogram parameters. Around 23% of cases presented clones in only one or two of the three evaluated cellular populations. Although our results represent a small sample, they can draw attention to the need for PNH investigation in individuals not belonging to the groups previously described with higher incidence or those showing alterations only in some other routine laboratory tests. In the case of rare diseases, clinical suspicion is a crucial step in diagnosis. Communication between physicians and the laboratory is vital in some cases, as it is an effective method to detect small PNH clones. The number of positive cases might be higher than believed due to the lack of testing and studies using a sensitive method, although one with a high cost for Brazil's reality.