ABSTRACT:Relevance: To report a case of hypersensitivity to lamivudine, a medicine that is considered safe and is indicated as part of the initial therapy for HIV infected patients. Comments: It is reported the evolution of an HIV patient who developed a drug eruption due to the following antirretroviral therapy: tenofovir, lamivudine and efavirenz. It initially was attributed to efavirenz, due to its higher incidence in these adverse reactions and it was replaced by fosamprenavir/ritonavir. In spite of the replacement, the patient developed Stevens-Johnson's Syndrome. She was hospitalized and began a new therapy with atazanavir/ritonavir, followed by zidovudine and lamivudine and presented a drug reaction with the last one, which was considered to be the responsible for the hypersensitivity.