Background Glanzmann's thrombasthenia (GT) and Bernard-Soulier syndrome (BSS) are genetic bleeding syndromes characterized by defects in platelet aggregometry. Although these disorders are classified to be rare, their exact prevalence is still unknown; however, they are more frequent in communities where consanguineous marriages are common. Aim To study platelet surface glycoproteins expression using flow cytometry and to examine their correlation with bleeding severity using International Society of Thrombosis and Hemostasis–Bleeding Assessment Tools (ISTH-BAT) as bleeding score of choice. Patients and methods This case–control study included 51 patients with bleeding disorders recruited from the Department of Pediatric Hematology, Assiut University Hospital, in addition to 36 apparently healthy age- and sex-matched controls. All patients were tested for complete blood count (CBC), prothrombin time, partial thromboplastin time, platelet aggregation, and platelets surface glycoprotein analysis by flow cytometry. ISTH-BAT was used to register bleeding data for patients. Results GT and BSS had some similarities regarding the presentation and bleeding severity, but when CBC, platelet aggregation studies, and flow cytometric analysis were done, differentiation became much easier. GT patients showed a decrease in the expression of CD41 and CD61. Type I GT patients had more bleeding severity than type II and type III. BSS patients showed a decrease in expression of CD42b. There are correlations between the bleeding severity and CD41 in GT, and between the severity and CD42b in BSS. Conclusion Flow cytometric studies of platelet glycoproteins have great values in diagnosing BSS and GT, and further classifying GT cases into its three types. ISTH-BAT is a useful tool when dealing with platelet function disorders and has good sensitivity and ability to determine the severity.