Thirty-seven patients who were three to sixteen years old were managed with immobilization in a halo vest between 1987 and 1993. Twenty-four patients (65 per cent) had the halo vest applied in conjunction with operative arthrodesis of the cervical spine; the remaining thirteen patients (35 per cent) had the halo vest applied to immobilize the cervical spine after trauma. Complications occurred in twenty-five patients (68 per cent). Pin-site infections were the most common complications, developing in twenty-two patients. Grade-II infections (purulent drainage) developed more frequently in children who were eleven years old or more: they were identified in five of fourteen such patients, compared with two of twenty-three patients who were ten years old or less. There was a tendency toward more grade-I infections (non-purulent drainage, with or without erythema) and loosening of the pins in the children who were ten years old or less: eleven of twenty-three such patients had each of those complications, compared with four of fourteen children who were eleven years old or more. Both loosening and infection occurred more frequently at the anterior pin sites. Other complications included one dural penetration, one transient injury of the supraorbital nerve, and three pin-site scars that were considered by the family to be objectionable. There were no complications related to the vest part of the halo vest. Younger patients who had a halo construct with more than four pins (multiple-pin constructs) had a similar rate of complications compared with patients who were managed with a standard four-pin halo construct.(ABSTRACT TRUNCATED AT 250 WORDS)