Background: Human immunodeficiency virus (HIV) infection can be associated with oral mucosal diseases, including oral candidiasis and HPV infection, which are putative indicators of the immune status. Aim and Methods: This retrospective cross-sectional study was aimed at assessing the prevalence of HIV-related oral mucosal lesions in a cohort of Italian HIV+ patients regularly attending the Clinics of Infectious Diseases. Results: One hundred seventy-seven (n = 177) patients were enrolled and 30 (16.9%) of them showed HIV-related diseases of the oral mucosa. They were mainly found in male patients over 35 years old, undergoing Combination Antiretroviral Therapy (cART), and with CD4+ count < 500/µL. Oral candidiasis was the most common HIV-related oral lesion. No significant correlations could be detected between the prevalence of HPV infection and other clinical parameters (lymphocyte count, cART treatment and viral load). Conclusions: HIV-related oral mucosal diseases can correlate with immunosuppression. Early diagnosis and management of oral lesions in HIV+ patients should be part of the regular follow-up, from a multidisciplinary perspective of collaboration between oral medicine and infectious disease specialists, in an attempt to reduce morbidity due to oral lesions and modulate antiretroviral therapy according to the patient’s immune status.