ABSTRACT We report a case of mpox in an active duty male on board a naval warship, who presented with a chancre-like penile lesion and ulcerating lymphadenopathy in the setting of a nonreactive treponemal test. Despite empirical therapy for sexually transmitted infections, he developed a fever and a generalized pustular rash. The patient was placed in isolation, and contact tracing was performed. No further spread of mpox was identified despite close contact with multiple shipmates and a pet rabbit. This case highlights the obligation of medical providers who care for our military personnel and veterans to offer JYNNEOS vaccine to high-risk individuals. Additionally, with the rise in clade I mpox cases prompting a recent global health emergency declaration by the World Health Organization, it is essential to implement proper testing methods and treatments when considering mpox in the differential diagnosis because of its association with other sexually transmitted infections.