Persons infected with the human immunodeficiency virus (HIV) may have protean clinical manifestations. These characteristics have not been described for adult patients in Jamaica. This study was conducted to determine the clinical and epidemiological characteristics of adult and adolescent persons newly diagnosed with HIV presenting at a specialized clinic for sexually transmitted infections (STI). A retrospective analysis of the medical records of adult and adolescent patients newly diagnosed with HIV was undertaken over a 12-month period. The results showed that most patients (64%) were between 20 and 39 years old (age range 14–68 years, M:F ratio 1.4: 1). Heterosexual practice was admitted to by 77% of patients. At the time of presentation most patients (53%) were asymptomatic while 24% had some symptoms and 21% had acquired immunodeficiency syndrome (AIDS). The most common presentation was generalized lymphadenopathy (67%) which was significantly higher than skin rash (27%), oral candidiasis (24%), cough (24%), weight loss (24%) and pallor of mucous membranes (19%, p < 0.001). This study affirms that young people account for the majority of new cases of HIV infection. The heterosexual route was the predominant mode of transmission. Generalized lymphadenopathy was the commonest presenting feature of persons newly diagnosed with HIV infection.