The most serious adverse event caused by abacavir is the hypersensitivity reaction, which is usually associated with the presence of the human leukocyte antigen (HLA) subtype B*5701, as shown in recent studies. We describe the case of a 41-year-old Caucasian female patient, who tested HLA-B*5701 negative and developed fever and severe skin rash 10 weeks after the start of abacavir therapy. Similar reports suggest that not all severe abacavir-induced adverse events occur as a result of classic hypersensitivity reactions, and can present also in HLA-B*5701-negative patients.