A theoretical study has been carried out of the fragmentation of Na; ions following a collision with He. The collision leaves Na: in any of three electronic states, and each of these can fragment into three product channels (Na-2(+)+ Na, Na-2 + Na+ and Na + Na $ Na+). The Na-3(+) system has a conical intersection and an avoided crossing; these permit transitions between the different states. Cross-sections for each of the nine fragmentation pathways are presented for three different values of the initial vibrational excitation of Na-3(+) The cross-sections are very sensitive to this vibrational energy.