Loneliness is common in persons living with HIV (PLWH). Lonely people smoke at higher rates than the general population, and loneliness is a likely contributor to the ongoing smoking epidemic among PLWH. We explored factors associated with loneliness in a cohort of 272 PLWH smokers enrolled in two separate tobacco treatment trials. Loneliness was independently associated with lack of a spouse or partner, lower educational attainment, “other or unknown” HIV exposure category, depression, anxiety, recent alcohol consumption, and higher daily cigarette consumption. Referral to group therapy reduced loneliness whereas referral to an individual web-based tobacco treatment did not.