Partial cavo-pulmonary bypass (termino-lateral anastomosis between the superior vena cava and one of the pulmonary arteries) is an alternative to total cavo-pulmonary bypass because of a lower morbid-mortality, or a first step to this procedure. The authors report a retrospective study of 35 patients who underwent partial cavo-pulmonary bypass between November 1985 and October 1999 at the Geneva Children's Hospital with an average follow-up of 4 years. The mean age of the patients at the time of surgery was 6.4 years. Fourteen per cent of patients had tricuspid atresia, 37% had a single ventricle, 49% had an irreparable biventricular cardiopathy and 71% had already had a previous palliative procedure. There were 2 early and 6 late deaths. The 5 year survival was 71.2% and the 10 year survival: 62.3%. The commonest early complications were arrhythmias (11/35), chylothorax (9/35) and superior vena cava syndromes (9/35). The late complications observed were arrhythmias (4/35) and suboptimal function of the partial cavo-pulmonary bypass (7/35). Eighty eight per cent of patients were symornatically improved at one year (average NYHA Class 2.8 before and 1.7 after one year), and 40% of patients were asymptomatic at this time. The haematocrit decreased after partial cavo-pulmonary bypass but tended to rise again progressively to preoperative values after 9 years. Only 49% of survivors had not been reoperated 10 years after partial cavo-pulmonary bypass. Partial cavo-pulmonary bypass is therefore associated with a temporary improvement of symptoms and polycythaemia in children with complex cyanotic heart disease: later reoperation is often required.