The aim of the study was to evaluate the effectiveness of Tadalafil-SZ in treatment of erectile dysfunction in men suffering from type 2 diabetes mellitus or prediabetes. Two patient groups of thirty people with type 2 diabetes mellitus and prediabetes were identified. Patients mean age was 52.2 3.4 years and 48.5 2.8 years in groups with type 2 diabetes mellitus and prediabetes respectively. All patients suffered from erectile dysfunction, which significantly reduced their quality of life. To assess the erectile function, the ICEF (International Index of Erectile Function) and QoL (Quality of Life) questionnaires were used. Patients with prediabetes took Tadalafil-SZ 5 mg once a day for 3 months and patients with type 2 diabetes mellitus took Tadalafil-SZ 20 mg 2 times a week (Monday and Thursday) for 3 months as a treatment for erectile dysfunction. Results of this study showed that the administration of Tadalafil-SZ not only led to a significant improvement in the quality of life, a significant reduction in weight, body mass index, waist size in patients of both groups, but also led to a glycated hemoglobin level normalization without increasing the dose of glucose-lowering therapy in patients with uncomplicated type 2 diabetes mellitus and a pronounced decrease in morning insulin levels measured in the blood in patients with prediabetes. Almost half of patients in both groups increased testosterone blood level. According to the ICEF questionnaire, erectile function was significantly improved: in the group of patients with prediabetes: the ICEF-5 index prior to taking Tadalafil-SZ averaged 18.68 points (mild ED) whereas after taking the drug, a statistically significant increase in the ICEF index to an average of 23.02 points (p 0.05) was observed, which indicates the absence of erectile dysfunction in this group of patients during intake of Tadalafil-SZ. In the 2nd group of patients (with type 2 diabetes mellitus), the ICEF-5 index before treatment averaged 12.18 points, which reflects the average degree of erectile dysfunction, and at the end of the study there was a statistically significant increase in the ICEF-5 index to 18.44 points on average, which indicates a decrease in the severity of erectile dysfunction from moderate to mild (p 0.05). Overall Tadalafil-SZ is an effective treatment for erectile dysfunction in both patients with prediabetes and patients with type 2 diabetes mellitus.