Disclosure of HIV and other sexually transmitted infection (HIV/STI) testing history to sexual partners is low among gay, bisexual, and other U.S. sexual minority men (SMM). Patient portals (PP) could increase HIV/STI testing history disclosure. This study estimated the predictive validity of the Enhancing Dyadic Communication (EDC) latent construct for perceived behavioral intentions to use PP for HIV/STI test disclosures. A randomized subset of SMM completed the Patient Portal Sexual Health Instrument as part of the 2018 American Men's Internet Survey. Multivariable logistic regression models estimated associations between EDC and intentions to use PP for test disclosures. Among a sample of 1,509 SMM aged 15 to 77 years, EDC was associated with intentions to use PP to disclose test history with main partners (aOR 2.17; 95% CI 1.90 to 2.47) and non-main partners (aOR 2.39; 95%CI 2.07 to 2.76). Assessing EDC could be useful in clinical settings for interventions encouraging patients to communicate with partners about testing.