Dialects and accents in human speech have a demonstrated social function as markers of group identity and often serve as psychological foundations of trust and cooperation. The extent to which this phenomenon is a feature of primate communication more generally is still debated. Here, we show that the vocal signatures of bonobos, Pan paniscus, belonging to three social groups show group-specific acoustic features independent of genetic relatedness. We compared the barks of 22 adults from the three groups and found that individuals currently living together had more similar barks than individuals that had never met or had lost touch with each other, regardless of their degree of genetic relatedness. We concluded that group-specific vocal accommodation is present in bonobos, suggesting an early evolutionary emergence of vocal plasticity in apes, which could be a means to signal social closeness between individuals.