Neutrophil recovery has been implicated in deterioration of oxygenation and exacerbation of lung injury in pediatric oncology patients. Our objectives were to determine the impact of neutrophil recovery on oxygenation in pediatric oncology patients with acute hypoxemic respiratory failure (AHRF) and to identify risk factors that result in oxygenation worsening. A cohort of 24 neutropenic pediatric oncology patients with AHRF in whom neutrophil recovery occurred during a course of mechanical ventilation was evaluated. Oxygenation index (OI) and PaO(2)/FiO(2) ratio showed a trend of improvement after neutrophil recovery. Mean PaO(2)/FiO(2) pre-recovery was 205±48.67 versus 225±72.24 postrecovery (P=0.08), whereas mean pre-recovery OI was 9.39±0.96 compared with 8.31±1.1 postrecovery (P=0.078). Seven episodes (24% of the total episodes) of recovery were characterized by worsening of oxygenation. Tripling absolute neutrophil count on Day+2 compared with Day+1 postrecovery was associated with 28-fold increase in risk of oxygenation worsening. In conclusion, resolution of neutropenia lead to significant deterioration of oxygenation in 24% of episodes of neutrophil recovery in a pediatric oncology cohort with AHRF. Our findings suggest that a faster ANC increment in the 2 days after recovery is associated with an increased risk of oxygenation worsening.