The purposes of this study were to: (i) provide contemporary estimates of the prevalence of abdominal obesity, as assessed by waist circumference (WC), in Canadian adolescents and adults; (ii) provide estimates of the prevalence of abdominal obesity within normal weight, overweight and obese body mass index categories and (iii) examine secular changes in abdominal obesity. Data were based on three national health surveys conducted in 1981, 1988 and 2007–2009. WC was measured at the mid-point between the last rib and iliac crest in all three surveys. The prevalence of Canadians with abdominal obesity increased with age and was higher in females than in males. In 12- to 19-year-old adolescents, the estimated prevalence of abdominal obesity was 1.8% in 1981, 2.4% in 1988 and 12.8% in 2007–2009. The corresponding values for 20- to 69-year-old adults were 11.4%, 14.2% and 35.6%. Between 1981 and 2007–2009, mean WC values increased by 4.2 cm in adolescent males, 6.7 cm in adolescent females, 6.5 cm in men and 10.6 cm in women. Within the 2007–2009 survey, 2.6% of normal weight adults had abdominal obesity, 35.3% of overweight adults had abdominal obesity and 93.0% of obese adults had abdominal obesity.