The primary objective of this study was to evaluate in a random double-blind design, the sedative and behavioural responses of children undergoing outpatient paediatric dental procedures receiving either chloral hydrate (CH) alone or in combination with hydroxyzine. Forty American Society of Anaesthesiologists class I children (21 to 36 months of age) were randomly allocated to receive either 70 mg/kg CH alone or with 2 mg/kg hydroxyzine. The degree of crying, movement and overall behaviour was evaluated during treatment at different times. The combination of chloral hydrate/hydroxyzine (CH/H) significantly decreased crying and movement in relation to the effect induced by CH alone (p < 0.05) only at 45-60 min following the insertion of a rubber dam, whereas the overall behavior in both groups was no different throughout the dental procedures. In conclusion, our study demonstrated that hydroxyzine increased the effect of CH. However, because of the presence of high rates of oxygen desaturations and of deep sedation, careful use of this drug combination should be stressed.