Background:
Smoke free policies are increasingly being enacted in many countries. Lagos state recently passed a state-wide smoke free law. However, campuses were excluded from the list of public places where smoking would be disallowed. This study aimed to assess the second-hand smoke (SHS) exposure among university undergraduates and assess their support for smoke free campuses.

Methods:
This cross sectional descriptive study was carried out among 421 university undergraduates in the University of Lagos, being the largest university in the state, and respondents were selected using a multi stage sampling method. Data collection was by pretested self administered questionnaires. EPI INFO 7 software was used to compute descriptive statistics and frequency tables.

Results:
Majority (89.1%) were aware of the dangers of SHS and agreed that SHS was harmful to health. Many (55.4%) of the respondents agreed that students who are non-smokers have a right to inhale smoke free air on campuses and 57.1% felt irritated or angry (17.1%) when exposed to SHS on campus. Majority (80.1%) were in support of their university being smoke free and were in favor of banning smoking in any enclosed space on campus (79.6%). Exposure to SHS on campus was high, as one in five respondents were exposed to SHS in their hostel room (19.9%), in any other enclosed space on campus (19.7%), or in outdoor campus spaces(44.9%). Majority of the students exposed to SHS were non-smokers (92%).

Conclusions:
Most students are non-smokers but are exposed to SHS on campus. There is a huge support for smoke free campus policies among undergraduates, who are most affected by SHS on campuses. The state government should consider including campuses on the list of smoke free public spaces.