Five cases of Ki-1-positive anaplastic large-cell lymphoma diagnosed by fine-needle aspiration biopsy are reviewed, and cytologic, histologic, and ultrastructural findings in these cases are correlated. In all cases, the diagnosis of anaplastic large-cell lymphoma was suggested on the basis of the morphological appearance in aspiration smears. This diagnosis was confirmed by immunohistochemistry, which revealed strong positivity of most of the cells by Ki-1 antibody. Two of the lymphomas were T-cell type, one was B-cell type, and the remaining 2 were composed of null cells. In 2 cases, intracytoplasmic inclusions were seen in some of the tumor cells in aspiration smears. These were ultrastructurally correlated with large lysosomal bodies of variable morphology. Fine-needle aspiration combined with immunohistochemistry may be an effective technique for diagnosing this neoplasm. © 1992 Wiley-Liss, Inc.