The important risk factors of early initiation of smoking and alcohol drinking are: prosmoking family and peers, conduct disorders and delinquency, poor academic performance. The data obtained by physicians, teachers and children were collected at the age of 11 years. Children were divided into group A (without symptoms), Group B (with one or more symptoms). For statistic analysis, the programme EPI INFO was used.During the period between 7 and 11 years, new children with problematic behaviour (178=3.9%) were diagnosed in Group A, while substantial decreasing of children previously included in Group B was seen (by 59.1%). Together 7.05% of 11 years old children visited specialists (psychologists) due to their conduct disorders: 6.8% from Group A and 12.3% from Group B. Children more often than their teachers reported the frequent occurrence of conduct disorder. About 20% of children smoked, and more than 40% had tasted alcohol. However, the differences between Groups A and B were not significant. Our prospective study has demonstrated the possibility of misinterpretation of behavioural outputs. Children with previous behavioural problems had not a higher risk for early smoking and alcohol use.