To examine and compare trends in drinking prevalence in nationally representative samples of Swedish 9th and 11th grade students between 2000 and 2018. A further aim is to compare drinking behaviours in the two age groups during years with similar drinking prevalence. Data were drawn from annual surveys of a nationally representative sample of students in year 9 (15–16 years old) and year 11 (17–18 years old). The data covered 19 years for year 9 and 16 years for year 11. Two reference years where the prevalence of drinking was similar were extracted for further comparison, 2018 for year 11 (n = 4878) and 2005 for year 9 (n = 5423). The reference years were compared with regard to the volume of drinking, heavy episodic drinking, having had an accident and quarrelling while drunk. The prevalence of drinking declined in both age groups during the study period. The rate of decline was somewhat higher among year 9 students. In 2018, the prevalence of drinking was the same for year 11 students as it was for year 9 students in 2005. The volume of drinking was lower among year 11 students in 2018 than year 9 students in 2005. No differences were observed for heavy episodic drinking. The decline in drinking has caused a displacement of consumption so that today’s 17–18-year-olds have a similar drinking behaviour to what 15–16-year-olds had in 2005.