ObjectiveTo define reference ranges for the 3% oxygen desaturation index (DI3) in healthy children under 12 years old during sleep.DesignObservational.SettingHome.SubjectsHealthy children aged 6 months to 12 years of age.InterventionNocturnal pulse oximetry at home. Parents documented sleep times. Visi-Download software (Stowood Scientific) analysed data with artefact and wake periods removed.Main outcome measuresThe following oximetry parameters used in the assessment of sleep-disordered breathing conditions were measured: 3% (DI3) and 4% (DI4) oxygen desaturation indices—the number of times per hour where the oxygen saturation falls by at least 3% or 4% from baseline, mean saturations (SAT50), minimum saturations (SATmin), delta index 12 s (DI12s), and percentage time with saturations below 92% and 90%.ResultsSeventy-nine children underwent nocturnal home pulse oximetry, from which there were 66 studies suitable for analysis. The median values for DI3 and DI4 were 2.58 (95% CI 1.96 to 3.10) and 0.92 (95% CI 0.73 to 1.15), respectively. The 95th and 97.5th centiles for DI3 were 6.43 and 7.06, respectively, which inform our cut-off value for normality. The mean values for SAT50 and SATmin were 97.57% (95% CI 97.38% to 97.76%) and 91.09% (95% CI 90.32% to 91.86%), respectively.ConclusionIn children aged 6 months to 12 years, we define normality of the 3% oxygen desaturation index as <7 using standalone, motion-resistant pulse oximeters with short averaging times.