Background:
Studies of differences in cognitive function between smokers and non-smokers have yielded inconsistent results. However, most of studies have focused on middle-aged and elderly adults. The aim of our study was to examine the links between smoking status and cognitive function among vocational school students in Beijing, China.

Methods:
A total of 213 students aged 16- 20 (98 smokers and 115 non-smokers) were recruited from three vocational schools in Beijing. Participants completed three subtests of Wechsler Adult Intelligence Scale (WAIS) (information, arithmetic, digit span) and Dysexecutive Questionnaire (DEX). Participants who were smokers also completed a cigarette smoking questionnaire and Fagerstrom test for nicotine dependence (FTND).

Results:
Non-smokers performed better than smokers on the tests of arithmetic and digit span forward （P< 0.05）. They also had a lower total score of DEX and lower score on its three subtests (inhibition, knowing-doing dissociation and social regulation)（P< 0.05）.Smokers with mild nicotine dependence scored lower than smokers with moderate to severe nicotine dependence in the total score of DEX and in-resistance (one of subtests of DEX )（P< 0.05）. A positive but weak correlation exists between digit span backward and the age at start of smoking (r=0.262, P< 0.05).

Conclusions:
Smokers performed worse on some cognitive function (mental arithmetic reasoning ability, short-term attention and executive function) than non-smokers. It is not clear whether smoking exerts an adverse effect on cognitive function, or whether students with poorer cognitive skills are more likely to smoke.