Young sexual and gender minority (SGM) people assigned male at birth who use substances are at elevated risk of HIV acquisition. This brief report leverages a large cohort of SGM people assigned male at birth to estimate substance use homophily (i.e., same-same substance use status) in sexual partnerships. We found substance use homophily in this sexual network for marijuana, poppers, methamphetamine, and hallucinogens but not heavy episodic drinking, cocaine, or ecstasy. These results suggest substance use is associated with sexual network structure and may increase HIV disparities between individuals who do and do not use substances.