It is well established in legal and psychological research that combining multiple charges against a defendant into a single trial event has a tendency to increase the chance of conviction - this is known as the joinder effect. Legal scholars have long theorised that combining the trials of multiple defendants has a similar effect, disadvantaging co-accused by tainting them with guilt by association. However, little empirical evidence has been presented to support this. It has further been suggested that the joinder of co-accused defendants became more pronounced during the twentieth century, as judges in common law jurisdictions became increasingly reluctant to increase the courts' workload by severing trials. Drawing on a sample of prosecutions data from Victoria, this article explores the impact that being co-accused had on trial outcomes and the wider legal and sociohistorical issues surrounding such joint trials.