Chimpanzee introductions can be stressful and even dangerous for the individuals involved, and different facilities use different approaches to group formation. However, little empirical evidence has been available to evaluate the different factors related to successful or unsuccessful chimpanzee introductions. This study evaluated a variety of factors, such as age, sex, previous experience, and the behavior displayed during the initial introduction period, to determine any influence on the outcome of the introduction in 165 dyadic introduction events. The direct introduction of one chimpanzee to a group or to another individual resulted in an overall success rate of 86.7%. The first few social interactions were characterized by more aggressive and submissive behavior than afffiliative behavior, but this trend was quickly reversed. Unsuccessful outcomes were more common if wounding occurred, if either individual was male, and if the newcomer had high levels of submissive behavior. Among male chimpanzees, the behaviors during the first 10 min of the introductions were characterized by more submissive behavior of the newcomer and more aggressive behavior of the introduction partner. The frequency of aggression by the introduction partner was higher when the newcomer was introduced to one chimpanzee at a time rather than to the group as a whole. This information may have important consequences for how we view chimpanzee group formation, and factors such as previous experience and aggression may be less important than the method of introduction and the level of submissive behavior.