Internal infusion pumps are increasingly used as a safe method to deliver drugs in adult patients. However, a formal contraindication of this mode of therapy is the presence of a imbalance between the pump volume and the size of the abdominal wall as occurs in pediatric populations. We describe a method of implantation of an intrathecal infusion pump for baclofen therapy in a 10-year-old patient with cerebral palsy. Before the pump implantation we inserted a subcutaneous expander with a reservoir that was filled with saline solution every week. After three sessions, a pocket similar in size to an internal infusion pump was obtained. The result was a pump pocket with soft shaping and no edges that would not generate pressure sores or tissue tension after the pump insertion. This method could extend the use of internal infusion pumps in pediatric populations.