Although prominent theories of intimate relationships, and couples themselves, often conceive of relationships as fluctuating widely in their degree of closeness, longitudinal studies generally describe partners' satisfaction as stable and continuous or as steadily declining over time. The increasing use of group-based trajectory models (GBTMs) to identify distinct classes of change has reinforced this characterization, but these models fail to account for individual differences within classes and within-person variability across classes and may thus misrepresent how couples' satisfaction changes. The goal of the current analyses was to determine whether accounting for these additional sources of variance through growth mixture models (GMMs) alters characterizations of satisfaction changes over time. Applied to longitudinal data from 12 independent studies of first-married couples (combined N = 1,249 couples), GMMs that allowed for class-specific individual differences and within-person variability fit the data better than the GBTMs that constrained these to be equal across classes. Most notably, considerable within-person variability was evident within each class, consistent with the idea that spouses do indeed fluctuate in their satisfaction. Spouses who dissolved their marriages were 3.8-5.7 times more likely to be in classes characterized by greater volatility in satisfaction. Because the early years of marriage appear to be characterized by within-person fluctuations in satisfaction, time-varying correlates of these fluctuations are likely to be at least as important as time-invariant correlates in explaining why some marriages thrive where others falter. (PsycInfo Database Record (c) 2024 APA, all rights reserved).