An HTLV-I tax transgenic mouse model develops a syndrome with similarities to type 1 neurofibromatosis (NF-1). To investigate possible associations between this human retrovirus and NF-1, we have analyzed 67 neurofibromas from Japan (where HTLV-I infection is endemic) and compared them with 21 cases from the United States. We were not able to identify virus in tumor tissue in either group. This suggests that HTLV-I infection is not commonly associated with NF-1.