Upper respiratory (nose and throat) infections, ear infections and asthma are common among young children. This article uses data from the National Longitudinal Survey of Children and Youth (NLSCY) to trace trends in the prevalence of these conditions among young children in Canada from 1994/1995 to 2008/2009. Gender, age and regional differences in the occurrence of these conditions are examined, and possible links with exposure to cigarette smoke are considered. The prevalence of upper respiratory infections among children aged 2 to 3 remained constant or declined in most regions of Canada between 1994/1995 and 2008/2009, but rose significantly in Quebec. Ear infections declined significantly in all regions. The prevalence of asthma among children aged 2 to 7 rose steadily until 2000/2001 and then declined. A wide range of environmental factors, including reduced exposure to cigarette smoke, may have contributed to these trends.