This study aimed to provide a comprehensive characterisation of the indoor air quality during the sleeping period of 10 couples at Lisbon dwellings, using a multi-pollutant approach, and to understand how the compliance with legislation and guidelines was to assure a good indoor air quality. The assessment of indoor air quality was conducted in the cold season using real time monitors during the sleeping period for comfort parameters (temperature and relative humidity) and air pollutants (carbon dioxide e CO 2 , carbon monoxide e CO, formaldehyde e CH 2 O, total volatile organic compounds e VOCs, and particulate matter e PM 2.5 and PM 10), together with active sampling of bioaerosols (fungi and bacteria) before and after the sleeping period. Lower compliance (less than 50% of the cases) with the Portuguese legislation was found for temperature, CO 2 (3440 ± 1610 mg m À3), VOCs (1.79 ± 0.99 mg m À3) and both bioaerosol types. In 70% of the cases, PM 2.5 (15.3 ± 9.1 mg m À3) exceeded the WHO guideline of 10 mg m À3. All bedrooms presented air change rates above the recommended minimum value of 0.7 h À1 , highlighting that a good indoor air quality during sleep is not guaranteed.