There are few data on gynecomastia in HIV-infected children. Within the UK/Ireland's national cohort, 56 of 1873 (3%) HIV-infected children had gynecomastia, of which 10 (0.5%) were severe. All 10 had received antiretroviral therapy for a median of 27.5 (21, 42) months; 4 of 10 had received efavirenz, 7 of 10 and 6 of 10 had received stavudine and/or didanosine respectively. Five were nonreversible, despite changing antiretroviral therapy, and required breast reduction surgery.