Torsion of wandering spleen after the Fontan operation with situs inversus is rare.
Here, we report the case of a 6-year-old girl with a single ventricle and complete situs inversus who developed torsion of wandering spleen due to splenomegaly caused by post-operative haemodynamics of the Fontan operation. The platelet count was suggested to be useful in predicting splenic torsion.