Background. Disasters are believed to have large effects on the mental health of adolescents but the lack of prospective pre- and post-disaster data on affected and control populations have limited our knowledge on the validity of these claims. We examined the medium-term, 12 months' effects of a severe disaster on the mental health of adolescents, and compared them to effects after 5 months.

Method. A café fire in The Netherlands injured 250 adolescents and killed 14. We obtained data 15 months before and 12 months after the disaster about behavioural and emotional problems (using the Youth Self-Report) and substance misuse, in 124 students of an affected school of whom 31 were present at the fire (response 77·5%) and 830 other students (56·4%); mean age at baseline, 13·8 years.

Results. We found differences between students from the affected school and others for excessive use of alcohol (odds ratio 3·42, 95% confidence interval 2·00–5·85, p<0·0001), but not for behavioural and emotional problems and use of other substances. Effects had decreased compared to those after 5 months.

Conclusions. In the long run, the effects of disaster decrease regarding self-reported behavioural and emotional problems, but they remain regarding alcohol misuse among those present at the disaster, and their peers.