The National Bank of Denmark published a working paper using Danish administrative microdata on firms aged 0–65 to examine how firm size relates to firm age. While cross-sectional results show average firm size increasing with age, panel-based analysis finds size rises with age only for the first 10–15 years and then falls. Using fixed-effects estimation and a partial identification approach to the age-period-cohort problem, the paper points to sample composition as an important driver of cross-sectional patterns. It reports significant differences in exit rates by firm size, strong cohort effects for firms entering in the late 1950s, and evidence that exit rates are not monotonically decreasing with age.