Lymphadenopathy with no apparent cause had been reported in a group of women participating in a mammary tumor prevention program. A screening for retrovirus infection was organized to detect the virus as possible etiological agents. Data show a high percentage of positivity for HIV-1 among these lymphadenopathy patients, and surprisingly for HTLV-I, while no such positivity for either virus was found in matched controls or in patients where a different causal agent for lymphadenopathy was found. Of 26 seropositives, 23 deny any risk factor for HIV-1 and do not come from a HTLV-I known endemic area, but while it is impossible to exclude their knowledge of risk factors, it is worth noting that none of them presented a HTLV-I/HIV-1 double infection, which is very frequent in intravenous drug abusers, the major risk group in Italy. On the basis of these data spread of HTLV-I and HIV-1 appears to be more important in Italy than previously thought, and not confined to well-defined groups or, at least, among those who believe they do not belong to a risk group and therefore can represent a major vehicle for virus diffusion. Institution of screening for HTLV-I in blood donors should be taken immediately, and retrovirus infection risk criteria must be revised.