The assessment of positive affect (PA) and negative affect (NA) by means of the Positive Affect and Negative Affect Schedule has received a remarkable popularity in the social sciences. Using a meta-analytic tool--namely, reliability generalization (RG)--population reliability scores of both scales have been investigated on the basis of a random effects model in 147 studies. Correcting for measurement errors, the results demonstrate moderate to high internal consistency coefficients and variations of the PA and NA reliability scores with regard to time frame instructions, language of items, and sample characteristics. The percentage of PA and NA true score variance differs in subpopulations up to 11%. RG analysis of test-retest coefficients illustrates state-like fluctuations and trait-like stability of both scales. Calculations of the fail-safe number point at the robustness of the results. Applications of RG coefficients compared to single-study coefficients highlight the relevance of population coefficients for research and assessment situations. (Contains 2 figures and 4 tables.)