Infections are the main cause of morbidity and mortality in pediatric hematology and oncology (PHO) and hematopoietic cell transplantation (HCT) settings in children and adults. The analysis of incidence and outcome of bacterial, fungal, and viral infections in Polish PHO/ HCT centers was performed over a period of 72 months (2012–2017). The summary of infections in 5628 patients with newly diagnosed malignancy and 971 HCTs is presented in this paper. Additionally, data of 650 pediatric HCTs from 2012 to 2015 were compared with the data of 3200 HCTs in adults. The risk of any infection per patient was higher in HCT vs PHO patients (2062/971 vs 7115/5628; 2.1 vs 1.3; HR=1.7, p<0.0001). The incidence of bacterial infections was 34,2±0,6% in PHO vs 41,5±1,6% in HCT patients, and the outcome was better in PHO patients: 97,9±0,2% vs 91,8±1,0%. The incidence of patients with fungal infection was 8,8±0,4% vs 21,2±1,3%, and the outcome was better in PHO patients: 95,9±0,7% vs 85,8±2,3%. Incidence of viral infections was 5,0±1,0% in PHO setting, including part of previously transplanted patients, and 47,8±2,2% in HCT setting (60,9±2,3% allo-HCT; 5,6±1,3% auto-HCT). In children, the incidence was higher for bacterial (36.0% vs 27.6%), fungal (25.3% vs 6.3%), and viral (56.3% vs 29.3% allo-HCT; 6.6% vs 0.8% auto-HCT) infections than in adults (p<0.0001), and the outcome was better for bacterial (95.5% vs 91.4%), fungal (88.0% vs 74.9%), and viral (98.6% vs 92.3%) infections. In conclusion, the presented large studies have determined the incidence of infectious complications and their outcomes in HCT and PHO centers in Poland.