Onychomycosis in HIV-infected patients has a prevalence of 20-44% and is more frequently seen with CD4(+) T cell counts ≤450 cel μl(-1). There are case reports of improvement in onychomycosis after initiation of combined antiretroviral therapy (cART), but there are no prospective studies that prove the existence and frequency of this phenomenon. The aim of this study was to evaluate if HIV-infected patients with onychomycosis who begin cART improve and/or cure without antifungal treatment. We included HIV-infected patients with onychomycosis who had not started cART and nor received antifungal therapy during 6 months prior to the study. We evaluated affected the nails with the Onychomycosis Severity Index (OSI); nail scrapings were collected and direct microscopy with potassium hydroxide (KOH) as well as mycological culture were performed. We repeated these procedures at 3 and 6 months to assess changes. CD4 T cell counts and HIV viral load were obtained. A total of 16 patients were included, with male gender predominance (68.7%); distal and lateral subungual onychomycosis (DLSO) was the most common form (31.3%). Trichophyton rubrum was the most frequently isolated microorganism. OSI decreased 21.5% at 3 months and 40% at 6 months after initiation of antiretrovirals (P = 0.05). We found a non-significant tendency towards improvement with higher CD4(+) T cell counts and with viral loads <100 000 copies ml(-1). This could be due to the increase in CD4(+) T cells, decreased percentage of Treg (CD4(+)CD25(+)) among CD4(+) Tcells and/or a decreased viral load; further studies are necessary to prove these hypothesis.