Adverse drug reactions (ADRs) to antibiotics complicate the management of any infection, particularly opportunistic infections in advanced HIV as some ADRs are potentiated by HIV. Trimethoprim-sulfamethoxazole (TMP-SMX) causes ADRs in 40-80% of HIV infected individuals, compared to 3-5% in the general population. The incidence and severity of ADRs among HIV infected individuals appear to increase as they progress from latent infection to AIDS. We present a single case report of a 55-year-old African American male found to have an otherwise asymptomatic acute HIV infection who developed an ADR to TMP-SMX, despite having previously tolerating the medication. The proposed mechanisms for the increased incidence of sulfa hypersensitivity reactions among HIV infected individuals focus on either (1) HIV-induced changes in the immune function driven by falling levels of CD4 cells or (2) other HIV-specific factors correlated with rising viral load. To our knowledge this is the first reported case of new sulfa hypersensitivity in primary HIV and may provide clinical evidence to support the correlation between viral load and ADRs to TMP-SMX without a severely diminished CD4 count, though further research is necessary. This case also demonstrates a rare and easily overlooked presentation of HIV that may aid in early diagnosis.