T/null-cell anaplastic large cell lymphoma (ALCL) is a morphologically and clinically heterogeneous group of non-Hodgkin's lymphoma; to date several morphologic variants have been described on histologic specimens. However, the cytologic features of these variants in the fine-needle aspiration (FNA) specimens have not been well evaluated. The t(2;5)(p23;q35) has been identified in a subset of T/null-ALCL and is known to be associated with a favorable prognosis. We reviewed the cytomorphologic characteristics in 24 FNA specimens of ALCL. In all cases, the diagnosis was confirmed on histologic specimens, and immunohistochemical studies for anaplastic lymphoma kinase (ALK) protein expression were performed on the aspirates. The presence of ALK breakpoints were evaluated in nine cases, using a DNA break-apart probe on chromosome 2 covering the ALK gene by fluorescence in situ hybridization (FISH) techniques. Two hundred cells per case were examined. The results were expressed as the percentage of cells containing more than two signals of chromosome 2 to the total number of cells counted. FNA sites included lymph nodes (20), lung (2), breast (1), and soft tissue (1). The median age of the patients was 56 yr (range, 17–75 yr). Twenty cases had systemic involvement; in four cases, skin was the primary site with secondary involvement of the lymph nodes. All cases were CD30+ by immunohistochemistry; 20 were of T-cell phenotype and 4 were null cell type. The cytologic evaluation revealed typical anaplastic morphology (common type) with many “hallmark cells” in 16 (67%) cases. Other morphologic variants identified were small cell pattern in five cases, monomorphic pattern in two cases, and lymphohistiocytic pattern in one case. FISH studies showed that six (66.7%) of nine cases had at least two signals of chromosome 2, consistent with ALK breakpoints. With careful cytomorphologic evaluation in conjunction with appropriate immunohistochemical studies, a diagnosis of ALCL can be confidently made in the FNA specimens in the cellular aspirates and its morphologic variants also can be recognized. Furthermore, the FNA specimen is suitable in detecting ALK breakpoints by FISH study, permitting rapid identification of a subset of patients with ALCL, who may have a favorable prognosis. Using a commercially available probe, detection of ALK breakpoints in the FNA specimens is simple and can be a useful diagnostic adjunct in cases where distinction from other lymphomas or lymphoid lesions is morphologically difficult. Diagn. Cytopathol. 2003;29:61–66. © 2003 Wiley-Liss, Inc.