Treatment of neurologic decompression accidents consists of various hyperbaric oxygen (HBO) protocols. To facilitate such comparisons between different protocols we developed a gravity score. A group of 96 divers was used to establish the score. On admission we first identified signs and symptoms that had possible predictive value (chi 2 test). The parameters included were repetitive dive, clinical course before HBO, objective sensory disorder, motor impairment, and urinary disturbances. Each parameter was assigned a coefficient. The sum of the coefficients for each accident, based on the most severe manifestations before decompression therapy, yielded a score for each diver. A multivariate analysis was used to evaluate the overall agreement between the model prediction and clinical observations, which was 78.7%. A second group (66 divers) was used to validate the score; this group showed a significant difference in the gravity score between the divers who had sequelae and those who did not (P = 0.0001), and between the divers who had incapacitating sequelae and those who had mild sequelae (P = 0.04). Eighty-six percent of the divers with a score above 7 developed sequelae. This index remains to be validated in a prospective multicenter study. If endorsed, valid comparisons can be made between the different therapeutic protocols.