Interdependent relations and cooperation between criminal groups are found to be recurrent when studying illegal market activities specifically and organized crime generally. However, there is little systematic research into the level and characterization of how criminal groups co-offend with one another. Based on a case-study approach, this article examines structural co-offending patterns between differently ethnic-based criminal groups involved in an illegal drug distribution network targeted during a law-enforcement operation in Italy. Data was extracted from electronic and surveillance transcripts obtained from court documents, and analyzed using social network analysis (SNA) techniques. The results provide an insight into the structure and organizational features of group co-offending networks. They also offer an investigation into ethnicity within between-group criminal activity in Italy’s illegal drug trade. Implications for crime control strategies are discussed.