The aim of this study was to assess the exposure to second-hand smoke (SHS) in 90 primary health care centres in Catalonia, Spain. We conducted a cross-sectional study between March and October 2006. We measured vapour-phase nicotine as a marker of SHS in main halls, staff rooms, direction areas, and continued care. Sampler devices were exposed for 7 days, and samples were analysed by gas chromatography/mass spectrometry. We compared the median airborne nicotine concentrations with the non-parametric test for medians by sanitary region, sampled location, affiliation to the Smoke-free Primary Health Care Programme, and urban-rural area. From 300 sampler devices installed, 4 were lost, and detectable levels of nicotine were found in 89 samples (30.0%) in 48 different centres (53.3%). The overall median was 0.01 microg/m(3), with an interquartile range (IQR) of 0.01-0.07 microg/m(3). Median nicotine levels by locations were: reception hall 0.01 microg/m(3) (IQR: 0.01-0.06); staff room 0.01 microg/m(3) (IQR: 0.01-0.08); direction area 0.01 microg/m(3) (IQR: 0.01-0.01); continued care 0.01 microg/m(3) (IQR: 0.01-0.07). Results showed that airborne nicotine levels were very low, with 46.7% of primary health centres being free of SHS.