Purpose: The aims of this study were to investigate the occurrence of stuttering behavior across time and to evaluate the relationship between stuttering behavior and language ability in children with Down syndrome. Method: A national age cohort of Norwegian first graders with Down syndrome (N = 75) participated in the study. Speech samples from a story-retelling task and a picture book dialogue as well as standardized measures of vocabulary, grammar, and nonverbal mental ability were collected at two time points approximately 5 months apart. Stuttering behavior was evaluated through counting stuttering-like disfluencies and stuttering severity ratings. The relationship between stuttering behavior and language ability was investigated through hierarchical regression analysis. Results: The participants had stuttering severity ratings ranging from no stuttering behavior to severe and displayed all types of stuttering-like disfluencies. There were significant relationships between stuttering behavior and language ability at the first time point, whereas the relationships were not significant at the second time point. The stuttering severity ratings were significantly predicted by language ability across time, whereas the frequency of stuttering-like disfluencies was not. Conclusions: The occurrence of stuttering behavior was high across the measures and time points; however, the relationship between stuttering behavior and language ability varied across these variables. Thus, the nature of the relationship does not seem to follow a strict pattern that can be generalized to all children across time.