Background:
Young people are at a vulnerable stage of life that has been associated with initiation and addiction to tobacco and other substances. Street youths compared to their peers are prone to behavioural problems. However the association of smoking with occurrence of health-risk behaviour among street youths has been poorly documented. This study was conducted to determine the association between tobacco use and the occurrence of health-risk behaviours street youths in South-Western Nigeria.

Methods:
A community-based cross-sectional survey was conducted among 946 consenting street youths aged 15-25 years using multi-staged sampling technique. Independent association between tobacco use and other problem behaviours was assessed using logistic regression at 5% level of significance.

Results:
The mean age was 20.4 years (SD = 3.2), about two third were males and half of the study population were single with a partner. A higher proportion of street youths who had spent ≥ 1 year on the street were using tobacco compared to those that had spent < 1 year but it was not significant. Respondents with tobacco use had 9.3 higher odds of using marijuana (95% CI=4.3-20.2), 3.7 higher odds of using injectable drugs (95% CI= 1.2-12.0), 2.4 higher odds of having had sex under alcohol influence (95% CI=1.3-4.5), 1.8 higher odds of having unprotected sex (95% CI=1.0-3.1), 2.6 higher odds of having >10 sexual partners (95% CI=1.2-5.4) and 2.2 higher odds of having had sex with commercial sex worker (95% CI=1.2-3.9) but 3.3 times less likely to use kolanut (95% CI= 0.15-0.56).

Conclusions:
Tobacco use increases the risk of street youths engaging in other health-risk behaviours.