This paper presents results of an atmospheric particulate matter (PM) monitoring and source apportionment study conducted during summer and fall 2010 in Cairo. These results are compared to those of similar studies in 1999 and 2002. Concentrations of PM2.5 and PM10 mass and their chemical constituents were determined and chemical mass balance modeling was conducted to estimate the source contributions to ambient PM. Emphasis was placed on characterizing the long-term trends in atmospheric lead (Pb) concentrations and their sources in Cairo. PM2.5 and PM10 concentrations were highest during fall 1999 at four of the five study sites. This was also the case for open (vegetative/trash) burning contributions, which showed a smaller increase during fall 2010. Burning of agricultural waste after the fall harvest continues to be a major source of PM in Cairo. Both PM2.5 and PM10 mass decreased dramatically at Shobra, an industrial site, from 1999 to 2010. A reduction of lead smelting has resulted in a decrease of ambient Pb concentrations of up to two orders of magnitude from 1999 to 2010 at Shobra, El-Zamalek, and El-Qualaly. From 1999 to 2010, the mobile source contribution has been relatively stable at most of the study sites. Future efforts to reduce ambient PM should focus on controlling emissions from motor vehicles and open burning and implementing mitigation strategies for reducing resuspended road and construction dust.