We studied an 8 year-old girl whose height was 129 cm (25-50th percentile), weight 30 kg (75th percentile), blood pressure 115/75 mm Hg (75th percentile) and had a calcified mass lesion in the left posterior mediastinum. In the histopathological investigation of this mass lesion, symptoms of complicated atherosclerosis, such as mural thrombus and diffused calcification, were observed. Lipid investigations were performed in this patient whose total cholesterol and triglyceride levels were in the normal ranges. HDL-cholesterol, apoprotein A-I and alpha band were low without any other lipid and lipoprotein abnormalities. During one year, in her monthly lipid analysis the mean levels of HDL-cholesterol, apoprotein A-I and alpha band were found to be 0.73 +/- 0.11 mmol/l, 90 +/- 20 mg/dl and 23 +/- 5% respectively. Studies of her family revealed low levels of HDL-cholesterol, apoprotein A-I and alpha band in her mother and sister. We describe our investigation of this rare case of familial hypoalphalipoproteinemia.