<p>Chemsex refers to sexualized drug use among men who have sex with men (MSM). Chemsex practices lead to problematic substance use, but sexuality can also deviate toward loss of control and harmful consequences, leading to sexual addiction. However, the determinants of sexual addiction in chemsex have been poorly investigated so far. In a 353-individual sample of MSM seeking addiction treatment for problematic chemsex, sexual addiction was screened using the Sex Addiction Screening Test. Sociodemographic and clinical characteristics were also assessed, including an assessment of all drugs reported as problematic by participants, but also psychiatric history, including psychiatric hospitalizations, other medical conditions, and at-risk practices of chemsex (e.g., slam, that is, injection drug use), or previous history of overdose, respectively. Using a stepwise logistic regression model, we explored the factors associated with sexual addiction. Multivariable analyses found that, compared to other MSM, those with sexual addiction (<i>n</i> = 39, 11.0%) exhibited older age (per one-year increase: aOR = 1.04; 95% CI: 1.01–1.08), increased likelihood of previous psychiatric hospitalization (aOR = 2.95; 95% CI: 1.36–6.31), and problematic methamphetamine use (aOR = 6.00; 95% CI: 2.54–14.17), respectively. Some other parameters were associated with sexual addiction only in bivariable comparisons, such as less frequent problematic gamma-hydroxybutyrate/gamma-butyrolactone (<i>p</i> &lt; 0.05) and cathinone (<i>p</i> &lt; 0.01) use. In conclusion, sexual addiction among MSM with problematic chemsex was associated with increased psychiatric problems, but also with specific substance use patterns, especially a striking preeminence of problematic methamphetamine use.</p>