Three national proficiency scheme rounds on the analysis of volatile organic compounds (VOCs) in air have been organized; the first between April and June 2007, the second between May and July 2008, and the third between April and June 2010. A group of about 10 Italian laboratories used the U.S. Environmental Protection Agency Method TO-15 for the determination of VOCs in air collected in canisters. A canister containing a VOC mixture, prepared by dynamic dilution from certified reference materials, was shipped to each participating laboratory; VOC concentrations were between 2 and 50 parts per billion by volume. Homogeneity of the samples prepared was tested and considered adequate according to ISO 13528:2005(E); stability was also checked. The canisters were analyzed by the laboratories within 30 days by GC/MS. The data were analyzed by robust statistics. Good accordance among laboratory results was obtained.