Background: Large portion sizes have been associated with large energy intake, which can contribute to the development of overweight and obesity. Portion sizes of non-home cooked food have increased in the past 20 years, however, less is known about portion sizes of home-cooked food. Aim: The aim of the study was to assess if the portion sizes measured in calories in Danish cookbook recipes have changed throughout the past 100 years. Methods: Portion size measured in calories was determined by content-analysis of 21 classic Danish recipes in 13 editions of the famous Danish cookbook "Food" from 1909 to 2009. Calorie content of the recipes was determined in standard nutritional software, and the changes in calories were examined by simple linear regression analyses. Results: Mean portion size in calories increased significantly by 21% (β = 0.63; p < 0.01) over the past 100 years in the analyzed recipes. The mean portion size in calories from a composed homemade meal increased by 77% (β = 2.88; p < 0.01). The mean portion size in calories from meat increased by 27% (β = 0.85; p = 0.03), starchy products increased by 148% (β = 1.28; p < 0.01), vegetables increased by 37% (β = 0.21; p = 0.13) and sauce increased by 47% (β = 0.56; p = 0.02) throughout the years. Conclusions: Portion sizes measured in calories in classical Danish recipes have increased significantly in the past 100 years and can be an important factor in increased energy intake and the risk of developing overweight and obesity.