The more common oral lesions in patients with HIV or AIDS are: Candidosis, Hairy Leukoplakia, Kaposi's sarcoma, and non-Hodgkin's Lymphoma. Furthermore, there are some specific periodontal conditions that differ in clinical appearance compared with conventional gingivitis and periodontitis, such as Linear Gingival Erythema (LGE), Necrotizing Ulcerative Gingivitis (NUG), Necrotizing Ulcerative Periodontitis (NUP), and Necrotizing Ulcerative Stomatitis (NUS). NUP is characterized by gingivitis, LGE, or soft-tissue necrosis, in addition to spontaneous bleeding, severe pain, and (usually) a more rapid and extensive attachment loss with destruction and exposure of supportive bone. In Mexico, there are some studies that describe the prevalence and clinical characteristics of the oral alterations associated with HIV, such as NUG, at the time the syndrome is detected; nevertheless, there are no studies related to NUP at the same time. Objective: To determine the prevalence of NUP in patients with HIV/AIDS in the Infectology Department in a public hospital of Guadalajara, Mexico. Methods: Fifty-two patients with HIV/AIDS diagnosis and under antiviral treatment (age range, 17-68 yrs; nine female and 43 male) were included during a one-year period. The diagnosis of NUP was performed by periodontists through periodontal charting, including signs and symptoms of HIV/AIDS-related oral diseases. Results: None of the subjects was found to have NUP. Twenty-two subjects had been previously diagnosed with Candidosis. At the time of periodontal diagnosis, according to the Centers for Disease Control Classification, nine subjects were in category A, 34 in category B (these individuals had opportunistic infections, and most of them had Candidosis); and in category C were seven individuals, the majority of whom had pneumonia. Conclusions: In this study, we did not find NUP prevalence at the time of periodontal diagnosis, probably due to the fact that all patients were under antiviral treatment.