Smoke-free legislation in indoor public places has concentrated smokers in the areas outside building entrances or other outdoor areas. This study assessed the drift of second-hand smoke between outdoor and indoor areas of cafés and restaurants in Barcelona, Spain, and characterized the exposure on outdoor terraces. Using a cross-sectional design, we monitored vapor-phase nicotine in indoor areas and outside entrances simultaneously (n=47), and on some outdoor terraces (n=51). We computed the median nicotine concentration and interquartile range (IQR) to describe the data and performed multivariate analysis to describe nicotine concentration and its determinants. The overall median nicotine concentration indoors was 0.65 μg/m3 (IQR: 0.29–1.17 μg/m3), with significant differences based on the number of smokers at the entrance (p=0.039). At outside entrances, the overall median nicotine concentration was 0.41 μg/m3 (IQR: 0.21–1.17 μg/m3). The nicotine concentrations indoors and at the corresponding outside entrances were not significantly different, and the multivariate analysis confirmed the relationship between these variables. On terraces, the overall median nicotine concentration was 0.54 μg/m3 (IQR: 0.25–1.14 μg/m3), but it increased to 0.60 μg/m3 when a tobacco smell was perceived, 0.72 μg/m3 on closed terraces, 1.24 μg/m3 when there were >6 smokers, and 1.24 μg/m3 when someone smoked >20 min. Multivariate analysis confirmed the outdoor terrace area, the season, the type of enclosure, and the number of smokers as the most relevant variables explaining nicotine concentration (R2=0.396). These findings show that second-hand smoke exposure exists in indoor areas due to smokers smoking at the outside entrances. In addition, exposure may occur on outdoor terraces when smokers are present and the terrace is enclosed to some extent. Thus, the current Spanish law does not fully protect non-smokers from second-hand smoke and supports extending regulation to some outdoor areas.