Aim: To assess children's behaviour during dental treatment using Entonox. Method: A group of 86 children referred to the ICEDM due to uncooperativeness was recruited for study. Inclusion criteria: ASA (Physical Status Scale) score I, II, Frankl behaviour rating scale (FSB) score 2 during initial visit, no medical contraindications for Entonox administration, parental informed consent. The study sample characteristics: 46 boys (53.5%), 40 girls (46.5%) aged 3-12 yrs. FSB score was recorded during initial visit, dental treatment and follow-up visit (3 months later). The 4 grade scoring was used for assessing children's self-management of inhalation namely as easy, neutral, difficult and unacceptably difficult. The following variables were recorded: the patient's age and sex, new vs. established ones, fillings vs. extractions, Entonox-naive vs. Entonox-experienced ones, Entonox-naive vs. other conscious sedation experienced ones, absence/presence of amnesia after treatment. Chi-square test at the 5% level of significance was applied for calculation. Results: 6-12 aged managed self-administration of Entonox easier (p=0.03) than 3-6 aged. Behavioural change between the initial visit and follow-up visit: better cooperativeness 35 (40.7%), no change 47 (54.7%), worse cooperativeness 3 (3.5%). Differences in behaviour score: 3-6 yr olds vs. 6-12 yr olds: p=0.01, boys vs. girls: p=0.10, new patients vs. established ones: p=0.37, Entonox -experienced patients vs. Entonox-naive ones: p=0.02, other conscious sedation experienced ones vs. Entonox-naive patients: p=0.33, restorative treatment vs. extractions: p=0.78, amnesia in children treatment-naive vs. treatment-experienced ones: p=0,003. Conclusions: Entonox administration enhances children's cooperativeness during dental treatment and helps reduce dental fear during follow-up visits. Acknoledgement: Supported by program PRVOUK-P 28/LF1/6. Keywords: behavioural management, conscious sedation, children dental anxiety, nitrous oxide