Background:
Exposure to Second-hand smoke (SHS) is common in many countries but the magnitude of the problem is poorly described worldwide. Hence, there is less public awareness of its effects on health. This study aimed to assess the magnitude of exposure to SHS and public knowledge on its effects among adults in urban and rural settings in Zanzibar.

Methods:
A cross sectional study was conducted in Unguja Island of Zanzibar, Tanzania. Four hundred and seventy five heads of households were randomly selected and ten key informants were purposefully selected and interviewed. Household exposure to tobacco smoke was assessed based on responses about current smoking history among household members at home, working places and public transport. Descriptive statistics using SPSS (version 16.0) was performed. The proportion of households that reported exposure from tobacco smoke was obtained. Chi-square test was used to compare sets of nominal data; P-value of less than 0.05 was considered not significant, while thematic analysis was used to generate report for qualitative data.

Results:
Prevalence of daily exposure to tobacco smoke at work places was 19.6%, while exposure at home was 15.6% and 9.9% were exposed in public transportation. The urban population were more exposed daily to tobacco smoke at home (16.2%) than the rural (14.0%). There was statistical difference between rural and urban residents' exposure to second hand smoke in indoor workplaces (χ² = 2.32, df = 1, p-value=0.12). Exposure to tobacco smoke in public transport was higher among rural residents (15.8%) compared to urban (8.0%). Rural residents were more aware that tobacco smoke from other people may cause health effect to someone else.

Conclusions:
Exposure to SHS is a problem in Zanzibar. Policies prohibiting smoking in public and work places should be instituted, in order to protect employees and the general public from the effects of SHS.