PURPOSE: Epidemiological research of stuttering has frequently focused on children, with a relative paucity of population level data specific to adults. Prevalence data for adults are reassessed here, including a breakdown of whether stuttering is overt or covert, and whether onset was in childhood or adulthood. The engagement of adults who stutter with stuttering communities is also estimated. METHODS: Prevalence calculations were based on data from studies having the strongest designs, following the systematic review of Gattie, Lieven & Kluk (2024, this issue). Original data for engagement with stuttering communities were gathered from English language internet stuttering support groups, a national stuttering charity in the UK and a regional stuttering support group in Manchester, UK. RESULTS: Adult stuttering prevalence was estimated at 0.96% (95% CI 0.65, 1.44). This can be broken down to 0.63% overt stuttering (95% CI 0.46, 0.79) comprising 0.53% childhood onset and 0.10% adult onset
and 0.33% covert stuttering (95% CI 0.19, 0.58) comprising 0.28% childhood onset and 0.05% adult onset. Covert stuttering will have been overestimated, and may often be very mild. Engagement with stuttering communities was estimated at 0.99% internationally, 0.63% nationally and 1.01% regionally. Actual engagement will have been lower due to attrition and overcounting. CONCLUSION: The adult stuttering prevalence estimate of 0.96% is consistent with the widely-cited all ages stuttering prevalence estimate of 1%. Of adults who stutter, fewer than 1% engage with stuttering communities.