Intestinal intraepithelial T lymphocytes express the α E subunit of integrin αEβ7, which is detected by antibodies to CD103. Accordingly, within T-cell neoplasms, CD103 reactivity has most frequently been reported in enteropathy-associated T-cell lymphomas, which are postulated to arise from intestinal intraepithelial T lymphocytes. However, prior studies of CD103 expression in T-cell neoplasms have been limited by the requirement for fresh or frozen tissue, given the historic lack of an antibody to CD103 for use in paraffin-embedded sections. Thus, a thorough assessment of CD103 expression in a broad spectrum of T-cell neoplasms as categorized by the current classification system has not yet been performed. This study uses a newly described antibody to define the profile of CD103 immunoreactivity in paraffin sections of a wide variety of T-cell neoplasms (184 cases). Overall, 22 T-cell neoplasms (12%) were CD103 positive, including 7 of 15 gastrointestinal lymphomas (3.8% of total cases; 46% of gastrointestinal cases). In intestinal cases, CD103 positivity did not correlate with morphology, presence or absence of enteropathy, or immunohistochemical profile. A history of celiac disease was not documented in any case. Frequent but inconsistent reactivity was also noted for adult T-cell leukemia/lymphoma with 4 of 10 cases (40%) positive. In the remaining T-cell neoplasms representing most entities within the current World Health Organization classification, CD103 reactivity was sporadically observed in 11 of 159 cases (6.9%). CD103 positivity is an unusual feature in T-cell neoplasms and tends to occur in gastrointestinal lymphomas and adult T-cell leukemia/lymphoma but is not a consistent characteristic of these neoplasms.