The aim of this study was to document the pharmacodynamics of chloral hydrate in former preterm infants at term post-conception age. The degree of sedation (COMFORT), feeding behaviour and cardiorespiratory events (bradycard-ic events, apnoeas) before and after administration of chloral hydrate (oral, 30 mg/kg) were prospectively eva-luated in former preterm infants during procedural sedation. Characteristics at birth, during neonatal stay and at inclusion were collected. Paired Wilcoxon and McNemar tests were used to study the impact of chloral hydrate. Characteristics of infants who displayed severe bradycardic events were compared to infants in whom no bradycardic events were recorded (MannWhitney U, Fischer’s exact). A significant increase in sedation (decrease COMFORT scale) was observed up to 12 h after administration. There was a minor but significant decrease in oral intake (161 to 156 ml/kg/day, P < 0.01). A significant increase in the number of bradycardic events (< 80/min: 38 to 82 events, of which < 70/min: 30 to 79 of which < 60/min: 15 to 45; at least P < 0.01) and in the duration of the most severe bradycardic event (8- 12.5 s) was observed. Therefore, further inclusion was stopped when 26 neonates were included. Infants who displayed severe bradycardic (< 60/min) events ( n=13) after administration of chloral hydrate had a lower gestational age at birth without difference in post-conception age at inclusion. Conclusion: Chloral hydrate was associated with an increase in unintended side-effects in former preterm infants, likely reflecting population specific pharmacodynamics and kinetics of chloral hydrate. The aim of this study was to document the pharmacodynamics of chloral hydrate in former preterm infants at term post-conception age. The degree of sedation (COMFORT), feeding behavior and cardiorespiratory events (bradycard-ic events, apnoeas) before and after administration of Characteristics of birth, during neonatal stay and at inclusion were collected. Paired Wilcoxon and McNemar tests were used to study the impact of chloral hydrate There was a significant increase in sedation (decrease COMFORT scale) was observed up to 12 h after administration. There was a minor but significant decrease in oral intake (161 to 156 ml / kg / day, P <0.01). A significant increase in the number of bradycardic events (<80 / min: 3 8 to 82 events, of which <70 / min: 30 to 79 of which <60 / min: 15 to 45; at least P <0.01) and in the duration of the most severe bradycardic event Infants who displayed severe bradycardic (<60 / min) events (n = 13) after administration of chloral hydrate had a lower gestational age at birth without difference in post-conception age at inclusion. Conclusion: Chloral hydrate was associated with an increase in unintended side-effects in former preterm infants, likely reflecting population specific pharmacodynamics and kinetics of chloral hydrate.