The morphologic features and immunophenotype of diagnostic nodal and bone marrow biopsy specimens were reviewed in 29 well-established cases of angioimmunoblastic T-cell lymphoma (AILT). All cases showed a characteristic polymorphous lymphoid and inflammatory cell infiltrate along with stromal-vascular changes. Perivascular aggregation or clustering of neoplastic clear cells was seen in only 41% of cases. Unique architectural changes, including extranodal extension (83%), follicular dendritic cell proliferation (93%), and a distinctly marginalized distribution of residual B cells (67%) were observed. Subsets of T cells with immunophenotypic abnormalities (CD10 coexpression or loss of pan-T-cell antigens CD3 and CD7) were identified in a majority of cases (96%). Significantly, these morphologic and phenotypic features were seen irrespective of the presence of an overt lymphomatous pattern. Bone marrow involvement was present in 90% of patients with available biopsy specimens. Our results indicate that unique morphologic alterations and subsets of phenotypically aberrant T cells are present consistently in nearly all cases of AILT, including morphologically less definitive biopsy specimens.