About thymic output, little is known in HIV-HCV co-infected patients. Thymic output can be measured by T-cell receptor excision circles (TREC) present in the so called "recent thymic emigrants" (RTEs). We have analyzed, by Real time PCR, sj-TREC+ cells in 11 patients with HIV-HCV co-infection; all patients were treated with highly active antiretroviral therapy (HAART), but were naive for interferon anti-HCV treatment. The results were compared with those of 21 age-matched normal donors. These data show no reduction of sj-TREC+ cells in co-infection. In 5 co-infected patients, IL-7 plasmatic levels were also evaluated by ELISA and no difference between co-infected patients and normal controls was found. Taken together, our data, although limited by the numerosity of the sample, may suggest that HCV co-infection does not affect the TREC/IL-7 pathway in HIV disease.