AbstractThree spindle cell neoplasms were encountered in a series of 46 FNA of the adrenal performed between 1984 and 1991. These neoplasms included a recurrent undifferentiated adrenal cortical carcinoma (ACC) with a predominant spindle cell pattern, a pheochromocytoma (PC), and a metastatic desmoplastic malignant melanoma (DMM), Cytologically, the ACC was characterized by the presence of numerous microtissue fragments composed of spindle‐shaped malignant cells with oval to spindle‐shaped nuclei, one or more nucleoli, and bipolar cytoplasmic processes. In some areas the tumor cells were dissected by vascular channels. The background contained abundant metachromatic stroma as well as individually scattered tumor cells. The PC was composed predominantly of loosely cohesive spindle‐shaped cells along with more polygonal shaped cells with delicate faintly staining granular cytoplasm. The tumor cells exhibited mild anisonucleosis. The tumor fragments were well vascularized by arborizing delicate capillary channels. The DMM was composed of microtissue fragments, interlacing fascicles and loose aggregates of spindle‐shaped malignant cells with hyperchromatic nuclei, small nucleoli, and an absence of cytoplasmic pigment. In each case ancillary studies including immunocytochemistry and electron microscopy (EM) were helpful in the differential diagnosis. The ACC was negative for cytokeratins, neuron‐specific enolase (NSE), and muscle‐specific actin (HHF), but displayed strong positivity for vimentin as welt as characteristic whorls of smooth endoplasmic reticulum by EM. The PC was positive for NSE and chromogranin with no EM performed. The DMM stained for S‐100 and vimentin but was negative for HMB‐45. cytokeratin, and HHF. EM examination revealed rare atypical premelanosomes. A discussion of spindle cell lesions of the adrenal gland encountered in FNA biopsy is presented along with the role of ancillary studies in the work‐up of these cases. © 1992 Wiley‐Liss, Inc.