Gastrointestinal stromal tumors are a group of neoplasms encompassing leiomyoma, leiomyosarcoma, and an epithelioid variant of leiomyosarcoma, as well as lesions expressing neural differentiation. These neoplasms are rare and account for 1% of all gastrointestinal tumors. With increasing frequency, fine-needle aspiration (FNA) has been used to diagnose intra-abdominal neoplasms before institution of definitive treatment. We encountered four patients with gastrointestinal stromal tumors diagnosed by FNA who ultimately underwent surgical excision of their tumors. The age of the patients ranged from 57 to 88 years. Smears from the aspirates were cellular and consisted of numerous small spindle cells distributed as cohesive fragments and individual cells. The dispersed cell population appeared largely as stripped nuclei. Several nuclei had perinuclear or paranuclear vacuoles, similar to the "halos" seen in sections. Cytologic evidence of malignancy (pleomorphism, nuclear irregularity, mitoses) were not identified in smears. Corresponding histologic sections demonstrated varying degrees of malignancy ranging from benign or low grade to frankly sarcomatous gastrointestinal stromal tumors. We conclude that the diagnosis of gastrointestinal stromal tumors can be made with a certain degree of confidence by using FNA findings. However, predictions about potential aggressiveness are best reserved for gross and histologic examination of the resected specimen.