The delayed rupture of the spleen in a 12-year-old boy is reported. He was admitted with an isolated blunt splenic injury. Successive echograms revealed an enlarging hypoechogenic region in the spleen. A magnetic resonance imaging (MRI) scan showed that this hypoechogenic region was a splenic pseudoaneurysm. On his 7th hospital day the pseudoaneurysm ruptured. An emergency laparotomy with splenorrhaphy was performed. His subsequent clinical course was uneventful and the pseudoaneurysm was replaced by a hematoma that eventually resolved.