To investigate the possible association between residential formaldehyde exposures and risk of cancer of the oro- and hypopharynx (OHPC, N = 205), nasopharynx (NPC, N = 27) and sinus and nasal cavity (SNC, N = 53), a population-based case-control investigation was carried out in 13 counties of western Washington. Controls (N = 552) were selected by random digit dialing. Subjects' residential histories, including type of dwelling, were determined from a structured telephone interview which also collected smoking, alcohol and demographic information. Multiple logistic regression was used to estimate exposure odds ratios (OR) while adjusting for known risk factors. A strong association was found between a history of having lived in a mobile home and NPC, but not OHPC or SNC. The NPC risk increased with the number of years lived in a mobile home: for those with 1 to 9 years the OR = 2.1 (95% confidence interval = 0.7-6.6), and for those with 10 or more years, the OR = 5.5 (95% CI = 1.6-19.4). No associations were found between any of the cancers and a history of exposure to new constructions containing particle board and plywood, or to urea-formaldehyde foam insulation. The association found with living in a mobile home must be interpreted with caution since it is based on a small number of cases, and may be due to factors other than formaldehyde. This report emphasizes the need for additional studies focusing on potential associations between indoor air pollutants and respiratory cancers.