OBJECTIVE During conversation, people tend to converge and become more similar across discourse characteristics, such as producing similar speaking turn lengths and even similar words. This "conversational synchrony" enhances social affiliation and rapport. Here, we investigated the role of the ventromedial prefrontal cortex (vmPFC) in conversational synchrony. We focused on the vmPFC because this region is strongly implicated in social behaviors related to synchrony, such as empathy. METHODS To examine the role of the vmPFC role in conversational synchrony, convergence of total words and words per turn were measured in the discourse of participants with bilateral vmPFC damage, healthy comparison participants (CP), and a brain-damaged comparison group with bilateral hippocampal damage (HPC) as they interacted with an unfamiliar partner. RESULTS CP and HPC interactions displayed convergence as the interactants' productions of words and words per turn became more similar across the sessions. In striking contrast, vmPFC interactions did not display convergence for either variable. A follow-up experiment revealed the same lack of convergence in the interactions of vmPFC participants with a more familiar conversational partner. CONCLUSIONS Our results suggest that vmPFC is a crucial part of the neurobiological system that supports the ability to synchronize conversational rhythms by dynamically adjusting behavior to the social environment.