Purpose It has long been known that stuttering behaviors vary across time and situation. Preliminary evidence suggests that this variability negatively affects people who stutter and that stuttering behaviors are more variable than adverse impact associated with stuttering. More information is needed to determine how variability affects people who stutter and what the clinical and research implications of variability may be. Method Two hundred and four adults who stutter participated in a mixed-methods study exploring (a) how variability of stuttering affects people who stutter in comparison to other aspects of the condition and (b) which aspects of the overall experience of stuttering are variable. Results Analyses indicated that variability is very commonly experienced by people who stutter and that it is among the most frustrating aspects of the condition. Qualitative analyses revealed that variability is experienced in all aspects of the stuttering condition, including the observable behavior other affective, behavioral, and cognitive reactions; and the adverse impact of stuttering. Notable individual differences were found in terms of which specific aspects of the condition were more variable for different respondents. Overall, analyses revealed that the variability of different aspects of stuttering can be viewed in a hierarchy from most variable to least variable: more external aspects (e.g., frequency, duration), more internal aspects (e.g., covert behaviors, physical tension), and cognitive-affective experiences (e.g., negative thoughts, feelings, and self-image). Discussion These findings suggest that variability is a common and burdensome aspect of the experience of stuttering and underscore the importance of considering variability in stuttering behavior, reactions, and impact in research, assessment, and treatment for adults who stutter.