Recebido em 8/10/09; aceito em 27/1/10; publicado na web em 3/5/10 OUTDOOR/INDOOR AIR QUALITY IN PRIMARY SCHOOLS IN LISBON: A PRELIMINARY STUDY. Simultaneous measurements of outdoor and indoor pollution were performed at three schools in Lisbon. Volatile organic compounds (VOCs), formaldehyde and NO 2 were passively monitored over a two-week period. Bacterial and fungal colony-forming units and comfort parameters were also monitored at classrooms and playgrounds. The highest indoor levels of CO 2 (2666 µg/m 3), NO 2 (40.3 µg/m 3), VOCs (10.3 µg/m 3), formaldehyde (1.03 µg/m 3) and bioaerosols (1634 CFU/m 3), and some indoor/outdoor ratios greater than unity, suggest that indoor sources and building conditions might have negative effects on air indoors. Increasing ventilation rates and use of low-emission materials would contribute towards improving indoor air quality.