HIV infection is a relative contraindication for allergic immunotherapy (AIT). In the last decade, highly active antiretroviral therapy (HAART) has improved the immune function and life expectancy in HIV-infected patients whose respiratory allergic incidence is similar to the general population. We evaluated the safety and clinical effectiveness of sublingual immunotherapy in a group of grass pollen-allergic HAART-treated HIV-positive patients. Thirteen patients received sublingual immunotherapy (SLIT) tablet (Oralair, Stallergenes©) and symptomatic therapy and were compared with nine patients receiving symptomatic therapy alone. Clinical benefits were evaluated by the analysis of total combined score (TCS), sum of symptom–medication score, and a quality of life (QoL) questionnaire. HIV viral load and peripheral TCD4 lymphocytes were analyzed at the beginning and at the end of the study. Clinical efficacy data showed a significant improvement in SLIT-treated patients compared to controls (TCS: P = 0.0001; QoL: P = 0.03). We did not observe any significant alteration of TCD4 cell counts and viral load (VL) in both groups. Our preliminary data showed that SLIT therapy in viro-immunological controlled HAART treated HIV positive patients was efficacious, safe and well tolerated.