Diagnosis of acute HIV infection (AHI) presents an opportunity to prevent HIV transmission during a highly infectious period. Disclosure is important during AHI as a means to facilitate safer sex practices and notify partners, particularly as those with AHI may be better able to identify the source of their infection because of the recency of HIV acquisition. However, little is known about disclosure during AHI. We conducted 40 semi-structured interviews with Malawians diagnosed with AHI (24 men; 21 married). Most participants reported disclosing to a sexual partner within a month of diagnosis, and knew or had a strong suspicion about the source of their infection. Participants often assumed their source had knowingly infected them, contributing to anger and feeling that disclosure is futile if the source already knew their HIV status. Assisted partner notification, individual and couples counseling, and couples HIV testing may facilitate disclosure during AHI. CLINICAL TRIAL REGISTRATION NUMBER:NCT01450189.