BACKGROUND Homozygous familial hypercholesterolemia (FH) is a rare disease with an incidence of 1 in 1 million births. It is characterized by blood cholesterol levels over 600 mg/dl and the development of extensive cutaneous xanthomata before the age of 5. Severe premature coronary artery disease results in fatal myocardial infarctions within the first two decades of life. The absence of LDL receptors makes homozygous FH resistant to treatment with most HMG-CoA reductase inhibitors, and alternative methods of removing cholesterol have been employed. METHODS We used the ASAHI plasauto-IQ double filtration cascade plasmapheresis to treat 2 young brothers aged 14 and 11 years and 6 months for 5 years and 1 month and 3 years and 10 months, respectively. The elder brother has received 136 double filtration treatments at 2-week intervals and the younger brother 100 such treatments without complications. RESULTS During the period of treatment the average pretreatment total serum cholesterol level for patient 1 was 442 mg/dl. The average posttreatment value was 163 mg/dl. The average fall in total serum cholesterol with each treatment was 63.2%. The mean total serum cholesterol for all the periods of treatment was calculated at 303 mg/dl. For the 2nd patient, the average pretreatment value of total serum cholesterol was 435 mg/dl. The posttreatment value was 124 mg/dl and the average fall 71.5%. The calculated mean total serum cholesterol for all periods of treatment was 280 mg/dl. CONCLUSIONS Double filtration cascade plasmapheresis at 2-week intervals provides an effective and safe long-term treatment for patients with homozygous FH. The achieved reduction in serum cholesterol allows complete resolution of cutaneous xanthomata, arrests previous atherosclerosis, and prolongs normal life.