Module Description: Medical complications are common among patients with opioid use disorder. Signs and symptoms of acute or chronic infectious diseases often prompt patients to seek medical care. The time of presentation for complications related to injection drug use present an opportunity to screen and employ early intervention strategies for other complications, engage individuals in addiction treatment and implement harm reduction. This module reviews features of skin and soft tissue infections among people who inject drugs, reviews risk factors for Hepatitis C (HCV) and HIV, describes prevention interventions for HCV and HIV, and discusses treatment approaches for HCV and HIV in patients with opioid use disorder.