Background: Only a limited number of studies have included objective measures of allergic sensitisation (such as skin-prick test [SPT] and serum specific IgE [sIgE]) when studying time trends in allergic respiratory disease in adults within the current millennium. Methods: Five health examination studies of random samples of individuals aged 18-69 years resident in the Copenhagen region were conducted in 1990-1991, 2006-2008, 2010-2011, 2012-2015, and 2016-2017. Allergic sensitisation was defined by sIgE (in 1990-1991, 2006-2008, and, 2012-2015) or SPT (in 2006-2008, 2010-2011, and 2016-2017) to at least one of the allergens: birch, grass, house dust mite, or cat. Allergic rhinitis was defined as sensitisation and self-reported nasal symptoms. Results: The age- and sex-standardised prevalence of sIgE-defined sensitisation increased from 16% in 1990-1991, to 26% in 2006-2008, and to 29% in 2012-2015. The age- and sex-standardised prevalence of SPT-defined sensitisation increased from 27% in 2006-2008, to 28% in 2010-2011, and to 32% in 2016-2017. Changes in sIgE-defined and SPT-defined allergic rhinitis showed similar increasing trends. Conclusion: The prevalence of allergic sensitisation and allergic rhinitis increased in a general adult Danish population over the last three decades and has thus continued to increase in the current millennium.