High frequency ventilation (HFV) is frequently used as a rescue therapy for ELBW infants with respiratory failure. The outcome of infants requiring rescue HFV remains an ongoing topic of investigation. Objective: to investigate the mortality and short term neurologic outcome of ELBW infants requiring rescue HFV. Methods: retrospective review of all infants<1000g cared for at a single level III NICU between 7/93-7/96, n=152. Infants receiving rescue HFV were compared to those not receiving HFV by Student's t-test and chi-square. Forward stepwise discriminant analysis was performed to account for potential confounding variables. All data are expressed as mean ± SD. Results: Overall, 144/152(95%) required mechanical ventilation. Of the 144 infants receiving mechanical ventilation 33 required rescue HFV (23%). Of the HFV group, 12 (36%) received high frequency jet ventilation (HFJV), 15 (46%) received high frequency oscillatory ventilation (HFOV) and 6 (18%) received both. The HFV group were lower birth weight (698 ± 153 vs 775 ± 150 g, p=.009) and lower gestational age (24.9 ± 2.1 vs 26.4 ± 2.3 wks,p=.0009) and more likely to have received surfactant (98% vs 78%, p=.01) compared to the non HFV group. There was no difference in the rate of administration of antenatal steroids between the groups. Mortality before hospital discharge was 58% in the HFV group vs 11% in the non HFV group (p<.00001). There was no difference in mortality based on the mode of HFV (HFJV=67%, HFOV=47%, both=67%). Of the infants surviving after HFV, there was no statistical difference in the incidence of grade 3-4 IVH and PVL (7% vs 7%,p=.9 and 7% vs 9%, p=.8, respectively) compared to the infants surviving after only conventional mechanical ventilation. After controlling for gestational age, birth weight and surfactant use by discriminant analysis, the need for rescue HFV remained associated with higher mortality (p<.00001). Conclusions: In our population of ELBW infants, the need for rescue HFV is associated with a 58% mortality. However, infants surviving after rescue HFV have the same low incidence of PVL and severe IVH as infants surviving after conventional mechanical ventilation. These data are important when counselling families of ELBW infants who require rescue HFV.