Although sensitive detection of pathological cognitive aging requires accurate information about the trajectory of normal cognitive aging, prior research has revealed inconsistent patterns of age-cognition relations with cross-sectional and longitudinal comparisons. Age trends in four cognitive domains were compared in over 5,000 adults with cross-sectional data, and in almost 1,600 adults with three-occasion longitudinal data. Quasi-longitudinal comparisons, which are similar to cross-sectional comparisons in that there is no prior test experience and are similar to longitudinal comparisons in that the participants are from the same birth cohorts, were also reported. The age trends in quasi-longitudinal comparisons more closely resembled those in cross-sectional comparisons than those in longitudinal comparisons, which suggests that, at least up until about age 65, age-cognition relations in longitudinal comparisons are distorted by prior test experience. Results from cross-sectional and quasi-longitudinal comparisons, which can be assumed to have minimal test experience effects, imply that normal cognitive aging is characterized by nearly linear declines from early adulthood in speed, and accelerating declines in memory and reasoning. However, vocabulary knowledge increased until the decade of the 60's in all three types of comparisons. (PsycINFO Database Record (c) 2019 APA, all rights reserved).