The authors present a case of echocardiographic diagnosis of a rare congenital cardiovascular anomaly in the form of mixed partial anomalous pulmonary veins connection in a 10-year-old girl with Turner syndrome and congenital mild stenosis of insufficient bicuspid aortic valve, made while diagnosing the causes of intestinal tract bleeding. The article presents various diagnostic difficulties leading to the delayed determination of a correct diagnosis, resulting from the absence of symptoms of circulatory failure in the early stage of the disease and the occurrence of severe and dominant auscultatory phenomena typical for congenital aortic valve defect which effectively masked the syndromes of increased pulmonary flow. The authors discuss the role of the impact of phenotypic characteristics of the Turner syndrome, in particular a short webbed neck restricting the suprasternal echocardiographic access and the presence of psychological factors associated with a long-term illness. The importance of indirect echocardiographic symptoms suggesting partial anomalous pulmonary veins connection in the presence of bicuspid aortic valve, e.g. enlargement of the right atrium and right ventricle, and paradoxical interventricular septum motion were emphasized in patients lacking ASD, pulmonary hypertension or tricupid and pulmonary valve abnormalities. The methodology of echocardiographic examination enabling direct visualization of the abnormal vascular structures was presented. Special attention was paid to the significance of highly sensitive echocardiographic projections: high right and left parasternal views in sagittal and transverse planes with patient lying on the side, with the use of two-dimensional imaging and color Doppler. Finally, the limitations of echocardiography resulting from the visualization and tracking of abnormal vascular structures hidden behind ultrasound non-conductive tissues were indicated, as was the role of other diagnostic modalities, such as angio-CT and/or nuclear magnetic resonance.